Examination of Grain Moisture Meters 

Using Air-Oven Reference Method 

Transfer Standards 

PART 1: Laboratory Grain Sample Preparation and Testing 

PART 2: Field Inspection and Evaluation

This publication is available free of charge 

from: http://dx.doi.org/10.6028/NIST.HB.159

NIST Handbook159

2016
INSIDE FRONT COVER - BLANK 
 

Examination of Grain Moisture Meters Using 

Air-Oven Reference Method Transfer 

Standards 

Part 1: Laboratory Grain Sample Preparation and Testing 

Part 2: Field Inspection and Evaluation

G. Diane Lee, Physical Scientist

Georgia Harris, Acting Chief

Office of Weights and Measures 

Physical Measurement Laboratory 

This publication is available free of charge from: 

http://dx.doi.org/10.6028/NIST.HB.159 

July 2016 

U. S. Department of Commerce 

Penny Pritzker, Secretary 

National Institute of Standards and Technology 

Willie E. May, Under Secretary of Commerce for Standards and Technology and Director 

NIST 159 Handbook 
Certain commercial entities, equipment, or materials may be identified in this document in order to 

describe an experimental procedure or concept adequately. Such identification is not intended 

to imply recommendation or endorsement by the National Institute of Standards and Technology, nor is 

it intended to imply that the entities, materials, or equipment are necessarily the best available for the 

purpose. 

National Institute of Standards and Technology Handbook 159, 2016 Edition 

Natl. Inst. Stand. Technol. Handb. 159, 2016 Ed., 78 pages (July 2016) 

WASHINGTON: 2016 
 

 

 

 

 

 

 

 

 

 

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Preface 

State and local weights and measures jurisdictions or other testing laboratories that use transfer standards 

developed using the air-oven reference methods (referred to as “air-oven reference standards) to test 

commercial grain moisture meters collect grains that are typically grown and traded in their State and 

transport them to their laboratory for testing. In the laboratory, these grains are cleaned, mixed, and tested 

to determine moisture content and test weight. The grains are then divided into smaller grain samples and 

assigned moisture and test weight reference values. 

These samples with known reference moisture and weight per bushel values are issued to weights and 

measures officials to test commercial grain moisture meters in accordance with NIST Handbook 44, 

Specifications, Tolerances, and Other Technical Requirements for Weighing and Measuring Devices, 

Section 5.56.(a) “Grain Moisture Meters.” Commercial grain moisture meters are meters that provide rapid 

measurement of grain moisture content during the sale of a quantity of grain. The moisture content of grain 

is used to determine the amount of money a seller will receive for the grain. For example, if grain moisture 

content is too high, the buyer must dry the grain before storage, so cost adjustments are made by the buyer 

to offset the cost for drying. Conversely, if the moisture is too low the grain quality may be affected and 

cost adjustments may be made for low moisture. 

This reference manual provides technical guidelines for: (1) laboratory grain sample preparation and 

testing; and (2) the field evaluation of grain moisture meters and multi-constituent grain analyzers that 

measure moisture in accordance with NIST Handbook 44, Section 5.56.(a) for field testing using air-oven 

reference method transfer standards. 

This manual is one of a number of manuals published by the National Institute of Standards and Technology 

that are designed to present, in compact form, comprehensive technical guidance for state and local weights 

and measures officials. Individual reference manuals for the various types of measuring devices in NIST 

Handbook 44 are being considered in acknowledgement of the rapidly developing technological character 

of commercial measurement and the ever-changing equipment used in the measurement process. 

Although this handbook is prepared primarily for use by State and local weights and measures officials, the 

information may also be useful to manufacturers and commercial and industrial establishments interested 

in evaluating grain moisture meters. 

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Acknowledgements 

Special thanks go to the following individuals and groups for their technical contributions, reviews, and
 

input in the preparation of this handbook:
 

National Type Evaluation Technical Committee (NTETC), Grain Analyzer Sector EPO Work Group:
 

John W. Barber, JB Associates
 

Cathleen Brenner, USDA, GIPSA
 

Randy Burns, Arkansas
 

Sid Colbrook, Illinois (Illinois Weights and Measures, Retired)
 

Bob Davis, Illinois
 

John Fecht, Nebraska
 

Richard Pierce, (USDA, GIPSA, Retired)
 

Fred Seeber, Shore Sales Company, Inc. 

Cheryl Tew, (North Carolina Weights and Measures, Retired)
 

Bob Wittenberger, (Missouri Weights and Measures, Retired)
 

Will Wotthlie, (Maryland Weights and Measures, Retired)
 

NIST Office of Weights and Measures Staff:
 

Tina Butcher
 

Linda Crown
 

References 

T. Butcher, L. Crown, R. Harshman, J. Williams, NIST Handbook 44 – Specifications and Tolerances and

other Technical Requirements for Weighing and Measuring Devices, latest edition.

USDA, GIPSA, Technical Services Division, Air-Oven Moisture Reference Laboratory Working 

Instructions, latest edition. 

USDA GIPSA, Moisture Handbook, January 1999. 

USDA, GIPSA, Equipment Handbook, October 1996. 

J. W. Barber, JB Associates, Grain Moisture Meters from Theory to Practice (slide presentation), 2001. 

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Acronyms 

CC ............................................................................................................ NTEP Certificate of Conformance
 

EPO............................................................................................................... Examination Procedure Outline
 

GA.......................................................................................................................................... Grain Analyzer
 

GIPSA...................................................................Grain Inspection Packers and Stockyards Administration 

GMM ........................................................................................................................... Grain Moisture Meter
 

Handbook 44 ..................................................... NIST Handbook 44, Specifications, Tolerances, and Other
 

Technical Requirements for Weighing and Measuring Devices
 

NCWM......................................................................... National Conference on Weights and Measures, Inc. 

NIST..................................................................................... National Institute of Standards and Technology 

NTEP ..................................................................................................... National Type Evaluation Program
 

OWM .......................................................................................................... Office of Weights and Measures
 

USDA............................................................................................................ U.S. Department of Agriculture
 

USNWG............................................................................................................... U.S. National Work Group
 

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TABLE OF CONTENTS
 

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PREFACE..................................................................................................................................... iii
 

ACKNOWLEDGEMENTS .......................................................................................................IV
 

REFERENCES............................................................................................................................IV
 

ACRONYMS ................................................................................................................................ V
 

PART 1: LABORATORY GRAIN SAMPLE PREPARATION AND TESTING................ 1
 

SCOPE .................................................................................................................................. 1
 

GENERAL GUIDANCE ON SAFETY ............................................................................. 1
 

DEFINITIONS ..................................................................................................................... 2
 equilibrate .............................................................................................................................................2
 

laboratory standard meters.................................................................................................................2
 

naturally moist grains ..........................................................................................................................2
 

parent sample........................................................................................................................................2
 

test weight..............................................................................................................................................2
 

working sample.....................................................................................................................................2
 

EQUIPMENT....................................................................................................................... 3
 

Breathing Apparatus............................................................................................................................3
 

Grain Sample Cleaning and Mixing Equipment ...............................................................................3
 

Automatic or Hand Sieves .........................................................................................................3
 

Dockage Tester ..........................................................................................................................3
 

Dividers......................................................................................................................................3
 

Test Weight per Bushel Equipment....................................................................................................4
 

Basic Air-Oven Test Equipment .........................................................................................................4
 

Analytical Balance .....................................................................................................................4
 

Glass Vacuum Desiccator ..........................................................................................................4
 

Laboratory Mill..........................................................................................................................5
 

Mechanical Convection (forced-draft) Oven .............................................................................5
 

Moisture Dishes (tins)................................................................................................................5
 

Thermometer..............................................................................................................................6
 

Top-loading Balance..................................................................................................................6
 

GENERAL............................................................................................................................ 6
 

Grain Handling.....................................................................................................................................6
 

Air-Oven Test Procedures ...................................................................................................................7
 

Test Weight per Bushel Procedures....................................................................................................7
 

PARENT GRAIN SAMPLE PREPARATION................................................................. 7
 Collection...............................................................................................................................................7
 

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Cleaning ................................................................................................................................................7
 

Storage and Labeling ...........................................................................................................................8
 

WORKING SAMPLE PREPARATION........................................................................... 8
 

Laboratory Conditions.........................................................................................................................9
 

Temperature:..............................................................................................................................9
 

Maximum Rate of Change:........................................................................................................9
 

Relative Humidity:.....................................................................................................................9
 

Preparing Working Samples for Testing............................................................................................9
 

TESTING THE WORKING SAMPLE............................................................................. 9
 

Laboratory Standard Meter Moisture Measurements......................................................................9
 

Reference Air-Oven Moisture Measurements ...................................................................................9
 

Laboratory Standard Meter Moisture vs. Reference Air-Oven Moisture Bias ............................10
 

..............................................................................................................................................................10
 

Requirement for Laboratory Standard Meter Moisture vs. Reference Air-Oven Moisture Bias
 

Determine the Test Weight................................................................................................................10
 

Records................................................................................................................................................10
 

Parent and Working Samples...................................................................................................10
 

Field Samples...........................................................................................................................11
 

SELECTING AND PREPARING OFFICIAL GRAIN SAMPLES............................. 11
 Official Grain Samples for Field Testing..........................................................................................11
 

Time Lapse..........................................................................................................................................13
 

RETESTING AND REUSING OFFICIAL GRAIN SAMPLES .................................. 13
 Retesting Samples...............................................................................................................................13
 

Reusing Samples.................................................................................................................................13
 

PART 2: FIELD INSPECTION AND EVALUATION .......................................................... 15
 

EPO NO. XX................................................................................................................................ 15
 

SCOPE ................................................................................................................................ 15
 

GENERAL GUIDANCE ON SAFETY ........................................................................... 15
 

DEFINITIONS ................................................................................................................... 16
 audit trail.............................................................................................................................................16
 

cereal grain and oil seeds ...................................................................................................................16
 

constituent ...........................................................................................................................................16
 

back-up sample...................................................................................................................................16
 

drop......................................................................................................................................................16
 

grain calibration .................................................................................................................................17
 

grain moisture meter..........................................................................................................................17
 

kind of grain........................................................................................................................................17
 

moisture content (wet basis) ..............................................................................................................17
 

opened..................................................................................................................................................17
 

official grain samples..........................................................................................................................17
 

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grain sample........................................................................................................................................17
 

security seal.........................................................................................................................................18
 

specification.........................................................................................................................................18
 

test site .................................................................................................................................................18
 

test weight............................................................................................................................................18
 

tolerance ..............................................................................................................................................18
 

warmed................................................................................................................................................18
 

FIELD EQUIPMENT AND GRAIN SAMPLES............................................................ 18
 

Apparatus and Equipment ................................................................................................................19
 

Breathing Apparatus ................................................................................................................19
 

Thermometer............................................................................................................................19
 

Container..................................................................................................................................20
 

Cooler ......................................................................................................................................20
 

Fire Extinguisher......................................................................................................................20
 

First Aid Kit.............................................................................................................................20
 

Portable Refrigerator................................................................................................................20
 

Grain Sample Racks.................................................................................................................21
 

Official Grain Samples ............................................................................................................21
 

Personal Protection Equipment (PPE) .....................................................................................22
 

Two-inch Aluminum Angle Gage............................................................................................22
 

Calculator.................................................................................................................................22
 

Safety Shoes.............................................................................................................................22
 

Security Seal ............................................................................................................................22
 

Approval Tags and Stickers .....................................................................................................22
 

INSPECTION..................................................................................................................... 23
 

General Consideration .......................................................................................................................24
 

Suitability, Installation, and Visibility of Identification ..........................................................24
 

Level ........................................................................................................................................25
 

Position of Equipment..............................................................................................................26
 

Location and Access ................................................................................................................26
 

Assistance ................................................................................................................................27
 

Use and Maintenance...............................................................................................................27
 

Determination of Quantity and Temperature ...........................................................................28
 

Operating Instructions..............................................................................................................29
 

Indicating and Recording Elements..................................................................................................29
 

General.....................................................................................................................................29
 

Design ......................................................................................................................................29
 

Selecting or Recording Grain or seed Type and Class.............................................................30
 

Operating Ranges and Temperatures .......................................................................................31
 

Electrical Power Supply...........................................................................................................34
 

Units and Readability...............................................................................................................34
 

Recorded Representation .........................................................................................................35
 

Provisions for Sealing..............................................................................................................35
 

Marking Requirements......................................................................................................................38
 

General Identification ..............................................................................................................38
 

Interchange or Reversal of Parts ..............................................................................................41
 

Marking, Operational Controls, Indications and Features .......................................................41
 

Values ......................................................................................................................................42
 

Permanence..............................................................................................................................42
 

On Devices that Indicate or Record in more than One Unit ....................................................42
 

Lettering...................................................................................................................................42
 

Other Devices not used for Commercial Measurements..........................................................43
 

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Measuring Element ............................................................................................................................43
 

Accessory Devices/Equipment ................................................................................................43
 

Current Calibration Data..........................................................................................................43
 

Figure 2-13. Calibration Data from a GMM Certificate of Conformance..................................................44
 

PRETEST DETERMINATIONS..................................................................................... 44
 

Grains and Constituents ....................................................................................................................44
 

Tolerances ...........................................................................................................................................44
 

How to Apply Tolerances ........................................................................................................44
 

TEST NOTES..................................................................................................................... 46
 

Official Grain Sample Maintenance, Test Methods and Documentation......................................46
 

Storage .....................................................................................................................................46
 

Official Grain Samples used for Field Testing.........................................................................46
 

Warming Official Grain Samples in Preparation for Testing...................................................46
 

Minimum Test and Maximum Number of Drops ....................................................................46
 

Preparation of the Official Grain Samples upon Arrival at the Test Site.................................47
 

Field Inspection and Test Method............................................................................................48
 

Documentation.........................................................................................................................48
 

Official Grain Samples (Transfer Standards), Minimum Test, Minimum Sample Size. .............49
 

TEST ................................................................................................................................... 50
 Minimum Test ....................................................................................................................................50
 

POST TEST TASKS.......................................................................................................... 52
 

Provisions for Sealing.........................................................................................................................52
 

Record Results ....................................................................................................................................52
 

Review Results ........................................................................................................................53
 

APPENDIX A. GRAIN MOISTURE METER SAMPLE TEST REPORT FORM ............. 1
 

APPENDIX B. GRAIN MOISTURE AIR-OVEN REFERENCE METHODS IN THE
 

UNITED STATES......................................................................................................................... 1
 

APPENDIX C. DETERMINING REFERENCE TEST WEIGHT PER BUSHEL VALUE
 

OF GRAINS .................................................................................................................................. 1
 

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Part 1: Laboratory Grain Sample Preparation and Testing 

Scope 

Part 1 of this Handbook provides: (1) technical guidelines for determining the moisture content of 

grain samples using reference air-oven test procedures; (2) a description of the laboratory equipment 

needed to determine the moisture in grain; and (3) instructions for preparing the parent and working 

samples used to test commercial moisture meters and multi-constituent grain analyzers in accordance 

with NIST Handbook 44, “Specifications, Tolerances, and Other Technical Requirements for 

Weighing and Measuring Devices,” Section 5.56.(a) “Grain Moisture Meters (GMM).” 

General Guidance on Safety 

Many policies and regulations will vary among jurisdictions. It is essential that inspectors or service 

persons be aware of all safety regulations and policies in place in the laboratory and to practice their 

employers’ safety policies. The safety reminders included in this manual contain general guidelines 

useful in alerting laboratory persons to the importance of taking adequate precautions to avoid 

personal injuries. These guidelines can only be effective in improving safety when coupled with 

training in hazard recognition and controls. 

Always be familiar with emergency procedures BEFORE testing. After an emergency has 

developed, crucial time can be lost if emergency procedures are not known. Be familiar with the 

procedures to follow in the event of an equipment malfunction or the development of a dangerous 

situation with the equipment or in the vicinity of the laboratory when operating specialized testing 

equipment. 

Be familiar with the nature of any product being dispensed by a device or being used in or near the 

laboratory. Know the emergency procedures to be followed when a spill of a hazardous product has 

occurred or a person has been exposed to the product. Knowledge of emergency procedures and 

related information should include the correct selection and use of fire extinguishers, the location of 

emergency shut-offs, and evacuation procedures. 

Keep a list of emergency phone numbers handy at all times in a notebook or on a card. Examples of 

numbers to keep are the local fire department, emergency medical facility, and other appropriate 

public safety agencies. Prior to testing, carefully check the laboratory for safety hazards and take 

appropriate precautions including: 

•	 Inspect all electrical cords and connections for damage to prevent electrical shock. 

•	 Learn the nature of hazardous products used in or near the laboratory. 

•	 Know the emergency evacuation routes for the laboratory. 

•	 Use personal protection equipment appropriate for the laboratory and for particular testing. 

•	 Wear safety shoes to prevent possible injury from falling weights, grain sample containers, 

and other equipment and to prevent slipping on wet or slick surfaces. 

•	 Wear proper breathing apparatus, if necessary, for protection from dust and other airborne 

contaminants. 

•	 Be sure that a first aid kit is available and that the kit is appropriate for the type of activity. 

•	 Practice safe and proper lifting techniques. 

•	 Use a lid opener if grain sample container lids are too tight to be removed comfortably by 

hand. Do not strain. Firmly grasp the container with good hand and wrist positioning; 

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•	 Dry condensation from the outside of the grain sample container to prevent slippage and 

possible breakage of container and/or injury to feet and toes; and 

•	 Watch for chips, cracks, or breakage of glass containers. If found, dispose of the container 

properly to prevent injury to the inspector. A damaged container may also affect the 

integrity of the grain sample moisture. 

Definitions 

equilibrate 

To be in or bring about equilibrium. In the case of preparing grain samples for moisture 

testing, it refers to uniform distribution of moisture in the grain samples. 

Note: Variations in moisture content may exist at the top, middle, and/or bottom of a onegallon working sample of grain. To reduce errors introduced by these variations, onegallon working samples of grain are not tested until they are refrigerated for at least 

72 hours; this allows any moisture variations within the grain sample to equilibrate. 

laboratory standard meters 

Grain moisture meters of each type of meter used commercially in the State that are 

maintained in the laboratory and used to select and/or screen grains for testing and field 

use. These meters are used to determine the moisture values of grain samples; these values 

are compared to the moisture results obtained using the air-oven reference method and 

cannot exceed 0.3 % if the grain sample is to be used to test the same moisture meter type 

in the field. Some laboratories also collect data on the laboratory meters that is shared with 

the meter manufacturer. 

naturally moist grains 

Grains that have not been artificially moistened by adding water to the grain after it has 

been harvested. 

parent sample 

The “parent sample” is a bulk sample of a given type of grain from which a “working 

sample” will be taken in order to create a set of official grain samples. 

test weight 

A measurement to determine the weight per volume (bulk density) of a particular lot of 

grain. For example, kg/hL or lb/bu. 

working sample 

The “working sample” is taken from a “parent sample” of grain and used to create a set of 

official grain samples. See Example 1. “Preparing Samples for One Inspector to Conduct 

Field Testing” in Part 1. Section 9.1. “Official Grain Samples for Field Testing.” 

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Equipment 

This list includes a brief description of the equipment used in grain sample cleaning and mixing, test 

weight determination, and air-oven testing. The USDA, GIPSA Equipment Handbook provides 

additional information to include maintenance of the equipment included in this list. Pictures 

(figures) are included to provide examples of equipment used in some laboratories. 

Breathing Apparatus 

A mask or other appropriate apparatus used to prevent excessive inhalation of dust or other 

contaminants. 

Grain Sample Cleaning and Mixing Equipment 

Automatic or Hand Sieves 

Automatic or hand sieves are used to remove 

larger or smaller materials from smaller samples 

of grain. See Figure 1-1. “Automatic or Hand 

Sieves.” 

Figure 1-1. Automatic or Hand 

Sieves. 

Dockage Tester 

This device automatically removes and separates smaller or 

larger materials from large portions of grain. State grain 

laboratories use dockage testers to clean large samples of 

grain. After running samples through the dockage tester the 

samples of grain are cleaner and more uniform in size. See 

Figure 1-2. “Dockage Tester.” 

Figure 1-2. Dockage 

Tester 

Dividers 

Dividers are used to reduce a parent sample of grain to 

smaller, representative working samples. When a sample 

is placed in the divider it is separated into equal parts. 

Dropping grain through the divider several times also 

mixes the grain samples so that a representative sample 

can be tested. See Figure 1-3. “Dividers.” 

Figure 1-3. Dividers 

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Test Weight per Bushel Equipment 

This equipment is used to determine the test weight 

per bushel of the grain sample that is weighed. 

Figure 1-4. “Test Weight per Bushel Equipment” shows 

an example of a scale in which one quart of a grain 

sample is weighed on the scale that is designed to 

multiply the weight by 32. Since there are 32 quarts to 

a dry bushel of grain, the scale provides a direct reading 

of the weight per bushel of the grain that is weighed. 

Figure 1-4. Test Weight per 

Bushel Equipment 

Basic Air-Oven Test Equipment 

Below is a list of basic equipment needed to perform single- and two-stage air-oven 

moisture testing and 72-hour air-oven tests for corn and beans. See Appendix B for 

additional information concerning air-oven test procedures. USDA, GIPSA Air-Oven 

Working Instructions provide a specific equipment list for each air-oven test described in 

the working instructions. 

Analytical Balance 

An analytical balance is used to take the final weight of 

the ground grain sample just before placing the samples 

in the oven for air-oven moisture testing and to get the 

weight of the sample after oven testing. The balance 

must be accurate to 0.1 mg. An example of an analytical 

balance is shown in Figure 1-5. “Analytical Balance.” 

Figure 1-5. Analytical 

Balance. 

Figure 1-6. Glass Vacuum 

Desiccator with a Porcelain 

Plate. 

Glass Vacuum Desiccator 

A desiccator is used for cooling moisture dishes and ground grain 

samples after oven testing. Cooling grain samples in a desiccator is 

necessary to prevent the dry grain from absorbing moisture from the 

atmosphere during the cool-down period. The desiccator must be of 

the glass vacuum type and have an inside diameter of approximately 

250 mm, with a porcelain desiccator plate. Activated alumina, 

“molecular sieves” Type 4A desiccant must be placed in the bottom 

of the desiccator. See Figure 1-6. “Glass Vacuum Desiccator” with a 

Porcelain Plate. 

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Laboratory Mill 

A laboratory mill is a device used to grind the grain 

sample in preparation for air oven testing. Studies 

have shown that the use of different types of mills 

yields different test results. The laboratory mill 

should be the type listed in the USDA, GIPSA Airoven Moisture Reference Laboratory Work 

Instructions: The Wiley Intermediate Model Mill 

with a 20 mesh (0.850 mm) opening (Arthur 

H. Thomas Company, Philadelphia, Pennsylvania). 

See Figure 1-7. “Laboratory Mill.” 

Mechanical Convection (forced-draft) Oven 

Ovens are used to dry grain samples at the 

temperatures that are specified in the USDA, GIPSA 

Air-Oven Working Instructions. Ovens must be 

capable of maintaining a uniform temperature within 

±1 °C of the oven temperature specified for the specific 

air-oven test being conducted. See an example of a 

“Mechanical Convection (forced draft) Oven” in 

Figure 1-8. “Mechanical Convection (forced-draft) 

Oven.” 

Figure 1-7. Laboratory Mill. 

Figure 1-8. Mechanical 

Convection (forced-draft) 

Oven. 

Moisture Dishes (tins) 

Moisture dishes are used to hold ground 

grain samples. The moisture dish with a 

ground sample of grain is place in an 

oven for a time period and temperature 

specified in the test procedure. The 

moisture dishes are constructed of heavy 

aluminum, with a diameter of about 

55 mm and a height of about 15 mm. For 

high moisture corn, moisture dishes with 

a diameter of 92 mm and a height of 

53 mm are needed. Intermediate size 

dishes with a diameter of 70 mm and a height of 30 mm may be used on large 

kernel samples. Follow the USDA, GIPSA air-oven working instructions (see 

Appendix B) to determine the correct size moisture dish for testing. The dishes 

must have fitted slip-in covers. Each individual dish and lid must be labeled 

with an identifying mark such as a unique number that is marked on both the lid 

and dish. Numbers engraved or stamped with a tool may be a better method for 

Figure 1-9. Moisture Dishes (tins). 

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marking the dishes. Clearly labeling lids and dishes allows for tracking the dish 

tare weights over time and for storing dish weights to eliminate the need for 

reweighing after each use. See Figure 1-9. “Moisture Dishes (tins).” 

Thermometer 

An ASTM No. 96C, NIST traceable, partial-immersion thermometer is used to 

measure oven temperature. These thermometers are placed in the opening at the 

top of the oven with the immersion mark aligned with the oven ceiling. See 

Figure 1-10. “Partial Immersion Thermometers.” For 72-hour, air-oven testing, 

laboratories may consider using thermometers with charting capabilities in 

addition to the partial immersion thermometers to ensure the oven temperature 

is consistent during the entire test. Partial-immersion or digital Thermometers 

are also used to determine grain sample temperatures. 

Figure 1-10. Partial-Immersion Thermometers. 

Top-loading Balance 

A top loading balance is used in grain sample preparation to weigh the required 

amount of grain that is placed in the moisture dishes for air-oven testing. The 

balance must be accurate to 0.01 g. Examples of these balances are shown in 

Figure 1-11. “Top Loading Balances.” 

Figure 1-11. Top-loading Balances. 

General 

Grain Handling 

When not required for immediate use, grain samples must remain in sealed bags or jars 

under refrigeration at a temperature of 1 °C to 3 °C (34 °F to 37 °F). Prior to use, samples 

must be allowed to equilibrate to room temperature ± 10 degrees of the ambient 

temperature before sample bags or jars are opened. This is necessary to prevent 

condensation which will have adverse effects on subsequent tests. 

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Air-Oven Test Procedures 

The laboratory must follow the air-oven test procedures in the USDA, GIPSA Technical 

Services Division, air-oven moisture laboratory working instructions. These procedures 

are included in training material provided by NIST, OWM or a copy may be obtained 

directly from: 

USDA, GIPSA, FGIS Telephone: 816-891-0401 

National Grain Center Fax: 816-872-1258 

10383 N Ambassador Drive 

Kansas City, MO 64153 

See Appendix B for additional information concerning air-oven test procedures. 

Test Weight per Bushel Procedures 

To determine the reference test weight per bushel value of grains, the laboratory must 

follow the test weight procedures in Appendix C of this reference manual. This procedure 

may also be downloaded from NIST, OWM website at www.nist.gov/pml/wmd/. Select 

the link titled “Weights and Measures Connection Newsletter,” then select the link titled 

“Newsletter Article Archives,” then select “Grain Moisture Meters/NIR,” then look for 

Series Number C-012 “Determining Reference Test Weight per Bushel Value of Grains.” 

Parent Grain Sample Preparation 

Grains used to test commercial grain moisture meters are collected from field locations within a 

weights and measures jurisdiction and brought to the jurisdiction’s laboratory. In the laboratory, the 

grains are cleaned and stored in appropriate containers in preparation for testing. This section 

describes collection, cleaning, and proper storage of this grain. 

Collection 

Parent samples of “naturally moist grains” are typically collected at harvest time for each 

grain that is typically grown and traded in a state’s jurisdiction. Low moisture and high 

moisture grain samples will be needed to test commercial grain moisture meters. As such, 

an attempt should be made to obtain samples covering a range of moistures for each grain 

type. (e.g., 13.0 % and 16.0 % moisture wheat samples). Low and high moisture ranges 

will vary per jurisdiction. Sufficient grain should be collected to provide enough samples 

needed to test all of the grain moisture meters in the jurisdiction. See Section 9, Example 1. 

“Preparing Samples for One Inspector to Conduct Field Testing” for guidance on the 

amount of grain to collect. 

Cleaning 

The parent samples are cleaned immediately upon receipt using dockage testers and 

automatic and/or hand sieves or equivalent grain or seed cleaning devices. Additional hand 

picking of the sample may be required to remove foreign material. Cleaned samples should 

consist of whole, sound seeds or kernels and be free of spoilage, dust, dirt, and foreign 

material. Follow the grain handling procedures in Part 1, Section 5.1. “Grain Handling” 

of this manual when cleaning the grain. 

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Storage and Labeling 

After samples are cleaned, mix each parent sample using a divider or other method to 

ensure that any portion of the parent grain sample is representative of the entire sample. 

After mixing, seal the grain in appropriate gallon storage containers (barrier, anti-static 

plastic bags or glass jars). See Figure 1-12. “Sample Storage-Glass Gallon Jars and Barrier, 

Anti-static Plastic Bags.” The samples are labeled with grain type, date of collection, 

collection point, and approximate moisture content and are assigned and labeled with a 

unique identification number for each grain sample. A number of jars or bags may be part 

of the parent sample so the unique identification number should include a sequential 

number following the identification number. For example, a unique ID number is 0714. 

Each jar or bag of grain with this ID number can be given the sequential number as follows 

0714-1, 0714-2, 0714-3, etc. denoting this is a part of the parent sample 0714. Place these 

samples in refrigeration for 72 hours at 2 °C to 4 °C (35 °F to 40 °F) prior to extracting 

working samples for testing to allow the moisture of the sample within the container to 

equilibrate. 

Figure 1-12. Sample Storage – Glass Gallon Jars and Barrier, Anti-static Gallon Plastic Bags. 

Working Sample Preparation 

Working samples are taken from a “parent sample” of grain and used to create a set of official grain 

samples. Since each gallon in the parent sample is representative of the entire parent lot, the first 

gallon working sample that is tested provides the information needed to determine if working 

samples within the parent sample lot can be used to create official grain samples. E.g., whether or 

not the parent sample meets laboratory standard meter moisture and reference air-oven moisture bias. 

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Laboratory Conditions 

When preparing and testing working samples, the laboratory must be maintained under the 

following conditions: 

Temperature: 

68 °F to 73 °F (20 °C to 23 ° C) 

Maximum Rate of Change: 

1.8 °F/hr (1.0 °C/hr) 

Relative Humidity: 

40 % to 60 % 

Preparing Working Samples for Testing 

When you have collected enough grain to make testing practical, which is typically when 

you have enough grain samples to test reference air-oven moisture and laboratory standard 

meter moisture within a workday, remove grain samples that have been refrigerated for at 

least 72 hours at the conditions specified in Part 1, Section 6.3. “Storage and Labeling.” 

Remove a one-gallon sample from each parent sample to serve as your working sample. 

Allow the sample to reach to within 10 degrees of the ambient temperature. Thoroughly 

mix each working sample by running it through a divider three times. 

Testing the Working Sample 

Each one-gallon working sample will be tested to determine a laboratory standard meter moisture; 

reference air-oven moisture; laboratory standard meter moisture vs. reference air-oven moisture bias; 

and test weight. Keep any remaining grain from the working sample in its original container (i.e., 

barrier, antistatic plastic bag or glass jar) during testing. 

Laboratory Standard Meter Moisture Measurements 

Determine the laboratory standard meter moisture of a sample from the one-gallon working 

sample selected for testing. Following meter manufacturers’ instructions, place an 

appropriate amount of the working sample in each of the laboratory standard meters. Test 

each gallon working sample three times on each laboratory standard meter and calculate 

an average laboratory standard meter moisture value for each gallon working sample and 

record the results. Then return the remaining sample used to obtain a laboratory meter 

moisture to its appropriate container. 

Reference Air-Oven Moisture Measurements 

Upon completion of the laboratory standard meter moisture measurement described in 

Part 1, Section 8.1. “Laboratory Meter Moisture Measurements,” immediately withdraw 

from each of the one-gallon working samples an amount sufficient to determine the 

reference air-oven moisture, as specified in the USDA, GIPSA air-oven test procedures. 

Record the average of three reference air-oven moisture results for each one-gallon 

working sample. See Appendix B “Grain Moisture Air-Oven Reference Methods in the 

United States” for additional information on the USDA GIPSA air-oven test procedures. 

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Note: Keep ground grain samples tightly sealed and limit the time between grinding and 

weighing the grain samples to reduce error in reference air-oven moisture results. 

Laboratory Standard Meter Moisture vs. Reference Air-Oven Moisture Bias 

Calculate the bias between the average laboratory standard meter moisture measurement 

and the average reference air-oven moisture measurement for each one-gallon working 

sample. Record the results and retain this information in your laboratory records. Mark 

the containers of all the working samples in the parent lot that meet the bias requirements 

in Part 1, Section 8.4. “Requirements for Laboratory Standard Meter Moisture vs. 

Reference Air-Oven Moisture Bias.” For example, an “A” that represents “Accepted” can 

be mark on the containers. Working samples and parent samples from which they were 

divided, which do not meet the criteria in Part 1, Section 8.4. “Requirements for Laboratory 

Standard Meter Moisture vs. Reference Air-Oven Moisture Bias” for all the laboratory 

standard meters may be discarded and record that the samples were discarded. 

Note: The laboratory standard meter moisture and reference air-oven moisture bias is only 

determined on a one-gallon working sample from each parent sample. The result of this 

test applies to the entire parent sample. 

Requirement for Laboratory Standard Meter Moisture vs. Reference AirOven Moisture Bias 

For any working sample, the difference between the average standard laboratory meter 

moisture and the average reference air-oven moisture result shall not exceed plus or minus 

0.3 % moisture. This bias is applied to each laboratory standard meter. 

Note: As meter technology improves (for example, the use of high frequency dielectric 

moisture meters with uniform algorithms across meters), variations between grain moisture 

meters will likely improve; however, grain variations may still influence meter moisture 

measurements. 

Determine the Test Weight 

While the reference air-oven testing is conducted, the working samples can be tested to 

obtain the test weight values. Test weight per bushel values are determined by following 

the procedures in Appendix C. “Determining Reference Test Weight per Bushel Value of 

Grains.” An average of 10 repeat test weight per bushel measurements is used to determine 

the test weight value for a working sample. 

Records 

Maintaining appropriate laboratory records provides an inventory of the grains and 

moisture ranges of those grains. This aids the laboratory in making any necessary changes 

to sample collection. Maintaining records of field data provides evidence of the integrity 

of the field samples. Records for all parent and working samples and field samples must 

be maintained in the laboratory. At a minimum, records must include: 

Parent and Working Samples 

a. grain type; 

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b. identification number; 

c.	 meter moisture result (the measurement of a one-gallon working sample applies 

to the entire parent sample lot); 

d. air-oven moisture results; 

e.	 meter moisture and air-oven moisture bias result (the measurement of a onegallon working sample applies to the entire parent sample lot); 

f. test weight results; and 

g. whether or not a parent sample lot was discarded after testing. 

Field Samples 

a. identification number of field samples issued; 

b. date field samples were issued; 

c. date field samples returned; 

d. retested oven results; and 

e. number of times field samples were warmed, opened, and dropped. 

Selecting and Preparing Official Grain Samples 

Make official grain samples from the one-gallon working samples that have an air-oven moisture vs. 

meter moisture bias that meets the requirements of Part 1, Section 8.4. “Requirements for Laboratory 

Meter Moisture vs. Air-Oven Moisture Bias” and were tested and have an assigned value for airoven moisture and test weight. The reference air-oven moisture and laboratory standard meter 

moisture bias is a one-time test and the values are assigned to all working samples within a parent 

sample based on the test results of a one-gallon working sample. But, it is necessary to test each 

gallon working sample within a parent sample for air-oven and test weight per bushel to avoid 

changes in moistures within the individual gallon working samples. These tests must be performed 

just prior to issuing the grain samples for field testing. 

Official Grain Samples for Field Testing 

Official grain samples used for field testing must be the grains that are representative of 

the grain types and moisture ranges normally traded in a jurisdiction. A one-gallon 

working sample of high moisture grain and a one-gallon working sample of the same grain 

type with a low moisture are selected for each grain type to prepare official grain samples. 

Each gallon working sample is divided into three or more official grain samples with a high 

moisture content and three or more official grain samples with a low moisture content for 

each grain type. (See Example 1. “Preparing Samples for One Inspector to Conduct Field 

Testing.”) 

Samples are prepared by following these Steps: 

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Part 1: Laboratory Grain Sample Preparation and Testing 

If the working samples are mixed and tested in accordance with Part 1, Section 8 “Testing 

the Working Sample,” on the same day that official grain samples are prepared, follow Part 

1, Section 9.1, Step c, below 

If the working samples were recently mixed and tested in accordance with Part 1, 

Section 8 “Testing the working sample” and then refrigerated, allow the sample to reach 

within 10 degrees of the ambient temperature, then follow Part 1, Section 9.1. “Official 

Grain Samples for Field Testing,” Steps a and c below. 

If there has been a significant lapse of time since a refrigerated working sample has been 

tested in accordance with Part 1, Section 8 “Testing the Working Sample,” repeat test in 

Part 1, Section 8.2. “Reference Air-Oven Moisture Measurements” and Section 8.5. 

“Determine the Test Weight” then follow Part 1, Section 9.1. “Official Grain Samples for 

Field Testing,” Step c, below. 

If it is the first time a working sample is tested, allow the sample to reach within 10 degrees 

of the ambient temperature, then follow Part 1, Section 9.1. “Official Grain Samples for 

Field Testing,” Steps a to c below. 

a.	 Thoroughly mix each gallon working sample for each grain type and moisture content 

by running it through a divider three times. 

b.	 Test the working sample in accordance with Part 1, Section 8.1. “Laboratory Standard 

Meter Moisture Measurements” to 8.5. “Determine the Test Weight” of this manual. 

c.	 Extract three grain samples of sufficient size from each grain type and moisture level of 

each working sample. Place the official grain samples in the appropriate containers (See 

Part 2, Section 4.1.9. “Official Grain Samples.”) and keep any additional portions for lab 

verification. Refrigerate the samples until distributed to field inspection staff. (See 

Example 1. “Preparing Samples for One Inspector to Conduct Field Testing.”) 

Example 1. Preparing Official Grain Samples for One Inspector to Conduct Field Testing. 

Working Grain 

Samples (Number 

of Gallons) Grain Type Moisture Content 

Field Samples – 

Number of Pint or 

Quart, Jars or Bags 

1 Corn 18.3 % (High) 3 

1 Corn 15.0 % (Low) 3 

1 Wheat 16.0 % (High) 3 

1 Wheat 13.5 % (Low) 3 

1 Soybeans 16.2 % (High) 3 

1 Soybeans 14.0 % (Low) 3 

Official grain samples must be of sufficient size for meter testing; this is typically one pint 

or one quart. Different meter models may require different sample sizes. Place the official 

grain samples in glass jars or poly bags and mark the official grain samples with the 

following information: 

a.	 working sample ID number; 

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b. grain type; 

c. date the official grain sample was prepared; 

d. reference moisture value (as determined by the USDA GIPSA Air-Oven Method); 

e. test weight value; and 

f.	 space for the inspector to record number of times the sample was warmed, opened, and 

dropped. 

Next, return the field samples and the remaining portion of the parent sample to 

refrigeration until needed by field inspectors. 

Time Lapse 

To prevent moisture loss and/or deterioration of the official grain samples that may occur 

over time, official grain samples should be issued to field inspectors as soon as practical 

after testing and preparation. If substantial time has elapsed from the initial determination 

of moisture and test weight measurements or there are concerns that these values have 

changed, another working sample from the parent sample should be tested to obtain a 

current moisture and test weight value and then used to prepare another set of official grain 

samples, prior to issuing the official grain samples for use in field testing. 

Retesting and Reusing Official Grain Samples 

Official grain samples are used for a limited number of drops when testing grain moisture meters as 

specified in Part 2, Section 7.1.4. “Minimum Test and Maximum Number of Drops,” Paragraph d. 

After a grain sample is used for the specified maximum number of drops, the samples must be 

returned to the laboratory for retesting and/or reuse. 

Retesting Samples 

In the event that problems or concerns arise with any field tests conducted with a given 

official grain sample, perform an air-oven test on those official grain samples returned to 

the laboratory. This will provide evidence of whether or not the official grain sample 

moisture was maintained during field testing. 

Periodically retest official grain samples that are returned to the laboratory after use to 

monitor and maintain a check on the system. If retesting reveals that moisture values are 

changing significantly, this may indicate a need to change field handling procedures; 

reduce the permitted number of drops; or take after actions to ensure that grain samples are 

maintaining their stability during field testing. 

Keep a record of all retest results and action taken to resolve issues resulting from retests. 

Reusing Samples 

Official grain samples may be reused if they are returned to the laboratory in good 

condition. To reuse these samples, recombine official grain samples of the same type and 

identification number in a gallon container and mix the grain. Next, place the sample in 

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refrigeration as specified in Laboratory Grain Sample Preparation and Testing, Part 1, 

Section 6.3. “Storage and Labeling.” After 72 hours, the working sample can be tested for 

reference air-oven moisture and test weight and then reissued as official grain samples. 

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PART 2: Field Inspection and Evaluation 

EPO No. XX 

Scope 

Part 2 of this Handbook provides technical guidelines for the field evaluation of grain moisture 

meters and multi-constituent grain analyzers that measure moisture in accordance with NIST 

Handbook 44, Section 5.56.(a) “Grain Moisture Meters” for field testing using air-oven reference 

method transfer standards. The requirements of NIST Handbook 44 are grouped into the following 

sections as outlined in NIST Examination Procedure Outlines: 

• Safety 

• Definitions 

• Equipment 

• Inspection 

• Pretest Determination 

• Test notes 

• Test 

• Post Tasks 

General Guidance on Safety 

Many policies and regulations will vary among jurisdictions. It is essential that the inspector or 

service persons be aware of all safety regulations and policies in place at the inspection site and to 

practice their employers’ safety policies. The safety reminders included in this manual contain 

general guidelines useful in alerting inspectors and service persons to the importance of taking 

adequate precautions to avoid personal injuries. These guidelines can only be effective in improving 

safety when coupled with training in hazard recognition and controls. 

Always be familiar with emergency procedures BEFORE beginning an inspection. After an 

emergency has developed, crucial time can be lost if emergency procedures are not known. Be 

familiar with the procedures to follow in the event of an equipment malfunction or the development 

of a dangerous situation with the equipment or in the vicinity of the inspection site when operating 

specialized testing equipment. 

Be familiar with the nature of any product being dispensed by a device or being used in or near the 

inspection area. Know the emergency procedures to be followed when a spill of a hazardous product 

has occurred or a person has been exposed to the product. Knowledge of emergency procedures and 

related information should include the correct selection and use of fire extinguishers, the location of 

emergency shut-offs, and evacuation procedures. 

Keep a list of emergency phone numbers handy at all times in a notebook or on a card. Examples of 

numbers to keep are the local fire department, emergency medical facility, and other appropriate 

public safety agencies. Prior to inspection and evaluation of a moisture meter carefully check the 

site for safety hazards and take appropriate precautions including: 

• Inspect all electrical cords and connections for damage to prevent electrical shock. 

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•	 Learn the nature of hazardous products used at or near the inspection site. 

•	 Know the emergency evacuation routes at each inspection site. 

•	 Use personal protection equipment appropriate for the site and for the particular job. 

•	 Wear safety shoes to prevent possible injury from falling weights, grain sample containers, and 

other equipment and to prevent slipping on wet or slick surfaces. 

•	 Wear proper breathing apparatus, if necessary, for protection from dust and other airborne 

contaminants. 

•	 Wear a hard hat for protection from overhead hazards, when appropriate. 

•	 Be sure that a first aid kit is available and that the kit is appropriate for the type of activity. 

•	 Practice safe and proper lifting techniques. 

•	 Use a lid opener if grain sample container lids are too tight to be removed comfortably by hand. 

Do not strain. Firmly grasp the container with good hand and wrist positioning. 

•	 Dry condensation from the outside of the grain sample container to prevent slippage and 

possible breakage of container and/or injury to feet and toes. 

•	 Watch for chips, cracks, or breakage of glass containers. If found, dispose of the container 

properly to prevent injury to the inspector. A damaged container may also affect the integrity 

of the grain sample moisture. 

•	 Be sure all equipment being transported by the inspector or service technician is properly 

secured in the vehicle. 

•	 Practice defensive driving when traveling between sites. 

Definitions 

audit trail 

An electronic count and/or information record of changes to the values of the calibration
 

or configuration parameters of a device. 

[NIST Handbook 44] 

cereal grain and oil seeds 

Agricultural commodities including, but not limited to, corn, wheat, oats, barley, flax, rice, 

sorghum, soybeans, peanuts, dry beans, safflower, sunflower, fescue seed, etc. 

[NIST Handbook 44] 

constituent 

A component of a grain, such as protein, oil, starch, or moisture that a grain analyzer is 

capable of measuring. 

back-up sample 

An official grain sample used only when a change is suspected in the moisture content of 

an official grain sample that will affect the test results. 

drop 

Each time a grain sample is passed through the measurement cycle of a moisture meter. 

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grain calibration 

A quantitative standardization established by a meter manufacturer for a specific grain and 

meter type. 

grain moisture meter 

Any device indicating either directly or through conversion tables and/or correction tables 

the moisture content of cereal grains and oil seeds. Also termed “moisture meter.” 

[NIST Handbook 44] 

Note: This Handbook is primarily oriented toward the preparation and use of samples for 

testing GMMs covered under NIST Handbook 44, Section 5.56.(a). However, Part 1 and 

some sections of Part 2 of this handbook may be used to develop official grain samples for 

use in evaluating meters that require conversion and correction tables to determine grain 

moisture content. Part 2, Sections 5.1. “Indicating and Recording Elements” to 9.Post Test 

Tasks” are requirements from NIST Handbook 44, Code 5.56.(a) and are not applicable to 

meters that require conversion and correction tables to determine grain moisture content. 

kind of grain 

Corn as distinguished from soybeans as distinguished from wheat, etc. 

[NIST Handbook 44] 

moisture content (wet basis) 

The mass of water in a grain or seed sample (determined by the reference method) divided
 

by the mass of the grain or seed sample expressed as a percentage (%).
 

[NIST Handbook 44]
 

opened 

Each time grain is removed from and returned to the sample storage container, it has been 

“opened” once. 

Note: The time required to change lids to enable thermometer insertion should be so short 

as not to constitute an opening. 

official grain samples 

Grain or seed used by the official as the official transfer standard from the reference 

standard method to test the accuracy and precision of grain moisture meters. 

[NIST Handbook 44] 

grain sample 

That portion of grain or seed taken from a bulk quantity of grain or seed to be bought or
 

sold and used to determine the moisture content of the bulk.
 

[NIST Handbook 44]
 

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security seal 

A uniquely identifiable physical seal, such as a lead-and-wire seal or other type of locking 

seal; a pressure-sensitive seal sufficiently permanent to reveal its removal; or similar 

apparatus attached to a weighing or measuring device for protection against or indication 

of access to adjustment. 

[NIST Handbook 44] 

specification 

A requirement usually dealing with the design, construction, or marking of a weighing or 

measuring device. Specifications are directed primarily to the manufacturers of devices. 

[NIST Handbook 44] 

test site 

A location housing a grain moisture meter or accessory device, which is subject to official 

inspection and testing. 

test weight 

A measurement to determine the weight per volume (bulk density) of a particular lot of 

grain. For example, kg/hL or lb/bu. 

tolerance 

A value fixing the limit of allowable error or departure from true performance or value. 

[NIST Handbook 44] 

warmed 

Each time a sample of grain is brought to within 10 oF of the ambient temperature, it has 

been “warmed.” 

Field Equipment and Grain Samples 

A brief description of the equipment needed for the field evaluation and testing of grain moisture 

meters are included in this section. Pictures (figures) are included to provide examples of equipment 

used in some states. See Figure 2-1. “Apparatus, Equipment and Documents for Field Testing of 

Grain Moisture Meters.” 

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Figure 2-1. Apparatus, Equipment, and Documents for Field Testing of Grain Moisture Meters. 

Apparatus and Equipment 

Breathing Apparatus 

A mask or other appropriate apparatus used to prevent excessive inhalation of 

dust or other contaminants. 

Thermometer 

Thermometers can be digital or liquid-in-glass and must meet NIST 

Handbook 105-6, “Specifications and Tolerances for Thermometers,” 

requirements. These thermometers are used to monitor the grain sample temperatures. 

(see Figure 2-2. “Examples of Thermometers”). A partial immersion thermometer is 

a thermometer that is designed to be used partially immersed in fluid or product 

typically to a designated immersion mark on the thermometer. If using a partialimmersion thermometer it should be placed into the grain sample to the 

submersion line on the thermometer. 

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Figure 2-2. Examples of 

Thermometers. 

Container 

A container of sufficient size may be used to safely carry accessory equipment. 

Cooler 

A cooler is needed for the sample jars of grain after removing the jars from the 

refrigerator. This will allow them to stabilize to ambient temperature and 

minimize exposure to temperature extremes and fluctuations. Ice must not be 

used in the cooler since it can cause condensation on sample jars and potentially 

affect the moisture content of the grain and stability of the sample. The cooler 

must be of adequate size to accommodate the number of samples that will be 

used for testing. See Figure 2-1. “Apparatus, Equipment, and Documents Field 

testing of Grain Moisture Meters.” 

Fire Extinguisher 

Know the proper use and selection of fire extinguishers for a given application. 

Contact your local fire department for current information and training. 

First Aid Kit 

An appropriate first aid kit should be maintained in your vehicle. Consideration 

should be given to the type of work that the inspector, or service person typically 

performs and the types of hazards typically encountered in these types of 

activities. Items in addition to those contained in a basic first aid kit may need 

to be added to address the potential hazards which may be encountered by the 

person who will be most likely to use the first aid kit. Check with your local 

OSHA office or with your departmental safety officer for input on the items to 

be included in each kit. 

Portable Refrigerator 

Portable refrigerators are used to keep the samples cold before and after testing 

to help maintain grain sample stability and condition. A connection to an energy 

source is needed to maintain cold conditions. For example, some portable 

refrigerators may be attached to the cigarette lighter in a motor vehicle. See an 

example in Figure 2-3. “Portable Refrigerator.” 

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Figure 2-3. Portable Refrigerator (front and side views). 

Grain Sample Racks 

Racks are used to carry standard grain samples from meter to meter during 

testing. 

Figure 2-4. Grain Sample Rack. 

Figure 2-5. Pint Grain Samples. Figure 2-6. Labeled Quart and Pint Grain 

Samples. 

Official Grain Samples 

At least three samples per grain type and moisture level (one high and one low 

moisture grain sample) are used to test meters; jurisdictions may choose to use 

additional official grain samples. The official grain samples must be stored in 

glass jars with lids or anti-static plastic bags. For additional details on 

preparation and handling of grain samples, see Part 1, Section 9.1. “Official 

Grain Samples for Field Testing” and Part 2, Section 7.1.2. “Official Grain 

Samples for Field Testing.” Examples of storage containers are shown in 

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Figures 2-5. “Pint Grain Samples” and 2-6. “Labeled Quart and Pint Grain 

Samples.” 

Personal Protection Equipment (PPE) 

The appropriate PPE for testing grain moisture meters may include goggles or 

safety glasses, hardhats, safety shoes, and other equipment deemed necessary by 

your organization to complete the tests. 

Two-inch Aluminum Angle Gage 

Use a ruler or other aid to verify the distance between the kettle and funnel height 

of the test weight per bushel equipment. A two-inch aluminum angle gage that 

rests on top of the kettle and maintains a perpendicular orientation to the top 

edge of the funnel is recommended as an aid in making this measurement. See 

Figure 2-7. “Aluminum Angle Gage” for an example of a gage used to measure 

the distance between the kettle and funnel height. 

Figure 2-7. Aluminum Angle Gage. 

Calculator 

A calculator may be necessary to assist with error and other test calculations. 

Safety Shoes 

Safety shoes to prevent possible injury from falling weights or equipment and 

also to provide protection from slippage 

Security Seal 

A uniquely identifiable physical seal, such as a lead-and-wire seal or other type 

of locking seal, a pressure-sensitive seal sufficiently permanent to reveal its 

removal, or similar apparatuses attached to a weighing or measuring device for 

protection against or indication of access to adjustment. 

[NIST Handbook 44] 

Approval Tags and Stickers 

Tags or stickers applied to grain moisture meters to indicate approval or rejection 

of the meter and may include the date of inspection. Devices may be tagged 

and/or removed from service due to large testing errors that exceed the allowable 

tolerances. 

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Inspection 

The most current requirements of NIST Handbook 44, Section 5.56.(a) must be applied when 

inspecting grain moisture meters in accordance with this manual. NIST Handbook 44, 

Section 5.56.(a) applies to all NTEP meters and meters manufactured or placed into service after 

January 1, 1998. Sections 5.1. “General Consideration,” to 9. “Post Test Tasks,” are the 

requirements of NIST Handbook 44, Section 5.56.(a) used to inspect and test grain moisture meters 

using air-oven transfer standards. 

Safety Reminders 

Location. 

• Carefully examine the inspection site prior to beginning an inspection and testing procedure. 

Look for potentially dangerous situations such as: 

o wet areas which may be slippery (see also Wet/Slick Conditions), 

o adjacent activities which may contribute a potential hazard to the inspection, 

o obstructions in the area which may prove to be safety hazards (e.g., objects on the ground 

which the inspector might trip over, objects in the path of the inspector to and from the 

device being tested, exits blocked by test equipment or vehicles, etc. – see also 

Obstructions), 

o pedestrian or vehicle traffic (see also Traffic), 

o steep or narrow stairways, 

o overhead hazards (e.g., feed bins, loading rack equipment, low-hanging beams in feed 

mills and warehouses, overhead activities, low doorways, etc. – see also Overhead 

Hazards), 

o lack of or defective handrails, and 

o loose or exposed wiring (see also Electrical Hazards). Use great care when moving 

around and working in areas in which these potential hazards are present. 

o When using flammable products (e.g., testing metering devices), note the location of the 

fire extinguisher, emergency shut-offs, etc. prior to beginning the inspection. 

Electrical Hazard. 

• Be particularly aware of potential electrical hazards in or near the inspection site when 

testing electronic devices or working in the vicinity of electrical equipment. 

• Loose or exposed wiring and a frayed or worn electrical cord should be brought to the 

attention of management at the inspection site. 

• Avoid standing on wet surfaces unless the electrical equipment is properly insulated and 

grounded. 

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Safety Reminders (continued) 

Obstructions. 

• Care should be taken to avoid injury from obstructions in the work area during the course of an 

inspection. Obstructions which might prove to be safety hazards include: 

o objects on the ground which the inspector might trip over, 

o objects in the path of the inspector to and from the device being tested, 

o steep or narrow stairways, and 

o exits blocked by test equipment or vehicles, etc. 

Overhead Hazards. 

• Note any overhead hazards such as feed bins, loading rack equipment, low-hanging beams in feed 

mills and warehouses, activities overhead, and low doorways prior to the inspection. 

• Take precautions, such as wearing a hardhat, to avoid potential injuries as the situation dictates. 

Wet/Slick Conditions. 

• Caution should be exercised when working in wet, slippery, or icy conditions to avoid slipping or 

possible injury from electrical sources. 

• Shoes with non-skid soles should be worn to provide adequate traction to prevent slipping. 

• Be sure all equipment being transported by the inspector or service technician is properly 

secured in the vehicle. 

• Practice defensive driving when traveling between sites. 

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General Consideration 

This section includes NIST Handbook 44 General Codes requirements used to determine 

if the device is suitable for its use; installed appropriately; and its markings are readily 

observable and understood. 

Suitability, Installation, and Visibility of Identification 

[Code References: NIST Handbook 44, Section 1.10. General Code, G-UR.1.1., 

G-UR.1.2., G-UR.2.1., UR.2. and G-UR.2.1.1.] 

Commercial equipment shall be: 

a.	 suitable for the service in which it is used with respect to the elements of its design 

including but not limited to its weighing capacity (for weighing devices), its 

computing capability (for computing devices), its rate of flow (for liquidmeasuring devices), the character, number, size, and location of its indicating or 

recording elements, and the value of its smallest unit and unit prices..................... 

.................................................................................................... G-UR.1.1., UR.2. 

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Guidance: 

□	 Current calibrations for a GMM are located in its Certificate of Conformance. 

Verify that the moisture meter has current grain calibrations for all grains being 

traded at the location. 

b.	 suitable for the environment in which it is used, including, but not limited to, the 

effects of wind, weather, and RFI........................................................... G-UR.1.2. 

Guidance: 

□	 Grain Moisture meters have specified operating conditions. Verify that a moisture 

meter is being used in accordance with the temperature ranges specified in the 

NTEP CC. 

□	 If there are sources of RFI near the moisture meter, look for any fluctuations in 

reading results during testing that affect the measurements. 

c.	 a device shall be installed in accordance with the manufacturer’s instructions, 

including any instructions marked on the device. A device installed in a fixed 

location shall be installed so that neither its operation nor its performance will be 

adversely affected by any characteristic of the foundation, supports, or any other 

detail of the installation........................................................................... G-UR.2.1. 

Guidance: 

□	 Review the manufacturer’s operating instructions to verify that the moisture meter 

installation is appropriate. 

d.	 equipment shall be installed in such a manner that all required markings are readily 

observable. ......................................................................................... G-UR.2.1.1. 

Guidance: 

□	 Ensure that you are able to view the marking such as serial number, model number 

and other identifiable markings needed to operate or identify the grain moisture 

meter. 

Level 

[Code References: NIST Handbook 44, Section 5.56.(a) GMM, S.2.3, UR.3.8.] 

A meter shall be equipped with a level indicator and leveling adjustments if its 

performance is changed by an amount greater than the applicable tolerance when 

the meter is moved from a level position to a position that is out of level in any 

upright direction by up to 5 % (approximately three degrees). The levelindicating means shall be readable without removing any meter parts requiring a 

tool. ..........................................................................................................S.2.3. 

a.	 If equipped with a level indicator, a meter shall be maintained in a level condition. 

..................................................................................................................... UR.3.8. 

Guidance: 

□	 Figure 2-8. “A Level Indicating Means Showing an In-level Condition” shows one 

type of level indicating means (a level bubble) on a grain moisture meter. Other 

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level indicating means may be available on grain moisture meters. Using the level 

indicating means on a meter, determine that the device is in level prior to testing. 

□	 If no level indicating means is available, place shims under the meter to raise it to 

a position out of level in any upright direction 5 % or approximately three degrees, 

then verify that the performance has not changed in the non-level condition. 

Figure 2-8. A Level Indicating Means Showing an 

In-level Condition. 

Position of Equipment 

[Code Reference: NIST Handbook 44, Section 1.10. General Code, G-UR.3.3., 

Section 5.56(a) UR.3.7] 

a.	 A device or system equipped with a primary indicating element and used in direct 

sales, except for prescription scales, shall be positioned so that its indications may 

be accurately read and the weighing or measuring operation may be observed from 

some reasonable “customer” and “operator” position. The permissible distance 

between the equipment and a reasonable customer and operator position shall be 

determined in each case upon the basis of the individual circumstances, 

particularly the size and character of the indicating element.... G-UR.3.3., UR.3.7. 

Guidance: 

□	 When grain is traded, grain samples are taken from truckloads of grain to 

determine its moisture content along with other dockage factors. Moisture testing 

is typically performed in a separate location. At this location verify that a customer 

is able to read the indications of the moisture meter and observe the measurement 

process. Also see Section 5.3.2. “Interchange or Reversal of Parts” below or NIST 

Handbook 44, Section 5.56.(a), S.1.1.(b) for minimum height requirements of the 

digits used to display moisture content. 

Location and Access 

[Code Reference: NIST Handbook 44, Section 1.10. General Code, G-UR.2.3.] 

a.	 A device shall be located, or such facilities for normal access thereto shall be 

provided to permit: 

1. the inspecting and testing of the device; 

2. the inspecting and applying security seals to the device; and 

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3.	 readily bringing the testing equipment of the weights and measures official to 

the device by customary means and in the amount and size deemed necessary 

by such official for the proper conduct of the test. 

b.	 Otherwise, it shall be the responsibility of the device owner or operator to supply 

such special facilities, including such labor as may be needed to inspect, test, and 

seal the device, and to transport the testing equipment to and from the device, as 

required by the weights and measures official........................................ G-UR.2.3. 

Guidance: 

□	 Grain moisture meters may be located in areas where it would be difficult to transport 

the official grain samples and other equipment necessary for testing. In these 

instances, the device owner must provide access for the inspector and his or her 

equipment so that testing can be performed. 

Assistance 

[Code Reference: NIST Handbook 44, Section 1.10. General Code, G-UR.4.4.] 

If the design, construction, or location of any device is such as to require a testing 

procedure involving special equipment or accessories or an abnormal amount of 

labor, such equipment, accessories, and labor shall be supplied by the owner or 

operator of the device as required by the weights and measures 

official...............................................................................................G-UR.4.4. 

Guidance: 

□	 If the design, construction, or location of a grain moisture meter requires special 

equipment to test the device, the device owner is responsible for providing the 

equipment needed to test the meter. For example, if the meter is located in a locked 

room, the device owner or operator must unlock the location or provide the inspector 

with keys to the room where the moisture meter is located. Likewise, if transporting 

the official samples requires an abnormal amount of labor or pose significant 

difficulty, the inspector can require assistance in transporting the equipment needed 

for the inspection. 

Use and Maintenance 

[Code Reference: NIST Handbook 44, Section 1.10. General Code, G-UR.4.1., 

G-UR.4.2., G-UR.4. and Section 5.56.(a) GMM, UR.3.1.] 

a.	 All equipment in service and all mechanisms and devices attached thereto or used 

in connection therewith shall be continuously maintained in proper operating 

condition throughout the period of such service. Equipment in service at a single 

place of business shall not be considered “maintained in a proper operating 

condition” if found to be in error predominantly in a direction favorable to the 

device user; or predominantly, equipment of the same type or application is found 

to be in error in a direction favorable to the device user. ...................... G-UR.4.1. 

b.	 Unstable indications or other abnormal equipment performance observed during 

operation shall be corrected and, if necessary, brought to the attention of 

competent service personnel. ................................................................ G-UR.4.2. 

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c.	 Weighing elements and measuring elements that are adjustable shall be adjusted 

only to correct those conditions that such elements are designed to control and 

shall not be adjusted to compensate for defective or abnormal installation or 

accessories or for badly worn or otherwise defective parts of the assembly. Any 

faulty installation conditions shall be corrected, and any defective parts shall be 

renewed or suitably repaired, before adjustments are undertaken. Whenever 

equipment is adjusted, the adjustments shall be so made as to bring performance 

errors as close as practicable to zero value............................................. G-UR.4.3 

Guidance: 

□	 All equipment must be maintained in proper operating condition. 

□	 Since calibrations for all NTEP meters are based on a national sample set and/or a 

uniform algorithm, the issue of setting equipment predominately favorable to the 

device owner may be more difficult to identify for grain moisture meters than for 

other devices such as retail motor fuel dispensers. However, if more than one type 

of meter is available, these meters should not be used to take advantage of the 

individual meter accuracy, such as buying grain on one type of meter where the 

accuracy of the meter is in favor of the device owner and selling grain on another 

meter type that would also benefit the device owner. 

□	 Adjustment shall not be made to compensate for malfunctions of the meter. These 

malfunctions and faulty operations such as inappropriate blinking of indications 

that may cause difficulty in obtaining a measurement or cause inaccurate reading 

must be corrected. Also any defective parts must be replaced. 

Determination of Quantity and Temperature 

a.	 The moisture meter system shall not require the operator to judge the precise 

volume or weight and temperature needed to make an accurate moisture 

determination. External grinding, weighing, and temperature measurement 

operations are not permitted. In addition, if the meter is capable of measuring test 

weight per bushel, determination of sample volume and weight for this 

measurement shall be fully automatic and means shall be provided to ensure that 

measurements of test weight per volume are not allowed to be displayed or printed 

when an insufficient sample volume is available to provide an accurate 

measurement................................................................................................... S.2.6. 

[Nonretroactive as of January 1, 2004] 

Guidance: 

□	 Some non-NTEP GMM moisture meters require a specific weight of grain and/or 

external temperature measurements (to apply a temperature correction) to determine 

the moisture content of grain. In order to eliminate some of the potential user errors 

associated with making these external measurements or grinding a grain, NTEP 

moisture meters must make these measurements automatically if they are needed. 

Verify that the meter does not require external measurements of temperature or 

weight or require the use of correction charts or tables to obtain a moisture 

measurement. 

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Operating Instructions 

a.	 Operating instructions are readily available to the user, service technician, and 

weights and measures official to include a list of accessory equipment and the 

kinds of grain or seed to be measured with the moisture meter. .................. UR.3.1. 

Guidance: 

□	 Some jurisdictions prepare a notebook which includes operating instructions along 

with the grains traded on meters in their jurisdiction. Although some jurisdictions 

may distribute this information, device owners are responsible for making 

information about their specific meters available to the inspector. 

Indicating and Recording Elements 

“Indicating and Recording Elements” refer to those NIST Handbook 44 code requirements 

that address requirements for how a grain moisture meter shall indicate and record the 

measurement results. It also includes the minimum abbreviations for the identification of 

the grain types on a moisture meter. 

General 

[Code References: NIST Handbook 44, Section 1.10. General Code, G.S.5.1.] 

All weighing and measuring devices shall be provided with indicating or 

recording elements appropriate in design and adequate in amount. Primary 

indications and recorded representations shall be clear, definite, accurate, and 

easily read under any conditions of normal operation of the device. ......G-S.5.1. 

Guidance: 

□	 The indications and recorded information on or from a grain moisture meter 

include the grain type, the percent moisture, weight per bushel, and the constituent 

label (moisture, protein, etc.) as appropriate, and may include other transaction 

information. This information must be clear, accurate, and easily read. 

Design 

[Code References: NIST Handbook 44, Section 5.56.(a) GMM, S.1.1.(a)-(g), S.1.2., 

Table S.1.2., S.1.3., S.1.5.] 

a. Meters shall be equipped with a digital indicating element........................ S.1.1.(a)
 

b.	 The minimum height for the digits used to display moisture content shall be 

10 mm. ....................................................................................................... S.1.1.(b) 

c.	 Meters shall be equipped with a communication interface that permits interfacing 

with a recording element and transmitting the date, grain type, grain moisture 

results, test weight per volume results, and calibration version 

identification............................................................................................... S.1.1.(c) 

d.	 A digital indicating element shall not display, and a recording element shall not 

record, any moisture content values or test weight per volume values before the 

end of the measurement cycle.................................................................... S.1.1.(d) 

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e.	 Moisture content results shall be displayed and recorded as percent moisture 

content, wet basis. Test weight per bushel results shall be displayed and recorded 

as pounds per bushel. Subdivisions of these units shall be in terms of decimal 

subdivisions (not fractions)......................................................................... S.1.1.(e) 

f.	 A meter shall not display or record any moisture content or test weight per volume 

values when the moisture content of the grain sample is beyond the operating range 

of the device, unless the moisture and test weight representations include a clear 

error indication (and recorded error message with the recorded 

representation). ........................................................................................... S.1.1.(f) 

g.	 On multi-constituent meters (e.g., meters which also measure grain protein), 

provision shall be made for displaying and recording the constituent label (such as 

moisture, protein, etc.) to make it clear which constituent is associated with each 

of the displayed and recorded values......................................................... S.1.1.(g) 

Selecting or Recording Grain or seed Type and Class 

[Code References: NIST Handbook 44, Section 5.56.(a) GMM, S.1.2., Table S.1.2.] 

a.	 Provision shall be made for selecting and recording the type and class or multiclass group (as appropriate) of grain or seed to be measured. The means to select 

the type and class or multi-class group of grain or seed shall be readily visible and 

the type and class or multi-class group of grain or seed selected shall be clearly 

and definitely identified. Abbreviations for grain types and multi-class groups 

indicated on the meter must meet the minimum acceptable abbreviations listed in 

Table S.1.2. “Grain Types and Multi-Class Groups Considered for Type 

Evaluation and Calibration and Their Minimum Acceptable 

Abbreviations.”............................................................................................... S.1.2. 

See examples of multiclass groups in table S.1.2. 

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Table S.1.2. 

Grain Types and Multi-Class Groups Considered for Type Evaluation and Calibration and 

Their Minimum Acceptable Abbreviations 

Grain Type Grain Class Minimum Acceptable Abbreviation 

Barley 

All-Class Barley* BARLEY 

Six-Rowed Barley SRB 

Two-Rowed Barley TRB 

Corn --­ CORN 

Grain Sorghum --­ SORG or MILO 

Oats --­ OATS 

Rice 

All-Class Rough Rice* RGHRICE 

Long Grain Rough Rice LGRR 

Medium Grain Rough Rice MGRR 

Small Oil Seeds 

(under consideration) --­ --­

Soybeans --­ SOYB 

Sunflower seed (Oil) --­ SUNF 

Wheat 

All-Class Wheat* WHEAT 

Durum Wheat DURW 

Hard Red Spring Wheat HRSW 

Hard Red Winter Wheat HRWW 

Hard White Wheat HDWW 

Soft Red Winter Wheat SRWW 

Soft White Wheat SWW 

Wheat Excluding Durum* WHTEXDUR 

Note: Grain Types marked with an asterisk (*) are “Multi-Class Calibrations.” 

[[Nonretroactive as of January 1, 1998] 

Guidance: 

□	 During accuracy testing verify that the meter is in compliance with the design 

requirement of NIST Handbook 44, Section 5.56.(a), S.1.1 (a)-(h) or Part 2. 

Section 5.2.2. “Design” of this manual to include minimum height for digits, 

display requirements, and minimum acceptable abbreviations used to identify 

grains. Also print a receipt and examine it for compliance. 

Operating Ranges and Temperatures 

[Code References: NIST Handbook 44, Section 5.56.(a) GMM, S.1.3.(a)-(d), 

UR.3.10.(a)-(d)] 

a.	 A meter shall automatically and clearly indicate when the operating range of 

the meter has been exceeded. The operating range shall specify the following: 

...............................................................................................................S.1.3. 

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1.	 Temperature Range of the Meter – The temperature range over which 

the meter may be used and still comply with the applicable requirements 

shall be specified. The minimum temperature range shall be 10 °C to 

30 °C. No moisture value may be displayed when the temperature range 

is exceeded. An appropriate message shall be displayed when the 

temperature of the meter is outside its specified operating 

range........................................................................................... S.1.3.(a) 

2.	 Temperature Range of each Grain or Seed –The temperature range for 

each grain or seed for which the meter is to be used shall be specified. 

The minimum temperature range for each grain shall be 0 °C to 40 °C. 

No moisture value may be displayed when the temperature range is 

exceeded. An appropriate error message shall be displayed when the 

temperature of the grain sample exceeds the specified temperature range 

for the grain. .............................................................................. S.1.3.(b) 

3.	 Moisture Range of the Grain or Seed – The moisture range for each grain 

or seed for which the meter is to be used shall be specified. Moisture 

and test weight per bushel values may be displayed when the moisture 

range is exceeded if accompanied by a clear indication that the moisture 

range has been exceeded............................................................ S.1.3.(c) 

4.	 Maximum Allowable Meter/Grain Temperature Difference – The 

maximum allowable difference in temperature between the meter and 

the sample for which an accurate moisture determination can be made 

shall be specified. The minimum temperature difference shall be 10 °C. 

No moisture value may be displayed when the maximum allowable 

temperature difference is exceeded. An appropriate error message shall 

be displayed when the difference in temperature between the meter and 

the sample exceeds the specified difference. ............................. S.1.3.(d) 

Guidance: 

□	 Meter operating ranges are included on the NTEP certificates of conformance. 

Figure 2-9. “Meter Operating Ranges Listed on a NTEP Certificate of 

Conformance” shows an example of operating ranges that are listed on a grain 

moisture certificate of conformance. Meter operating ranges are not typically 

verified in the field because meters will likely be maintained within their operating 

ranges. If conditions exist where these ranges can be verified, a test may be 

performed to ensure that the meter responds with the appropriate error messages. 

Operating Ranges: 

Ambient Temperature Range (Environment): 10 °C to 40 °C (50 °F to 104 °F)
 

*With Hardware/Software Modification 2 °C to 45 °C (35.6 °F to 113 °F)
 

Temperature Difference (Room to Grain Temperature): 20 °C (36 °F), see comments on page 3
 

Grain Temperature Range: 0 °C to 40 °C (32 °F to 104 °F)
 

Grain Moisture Range: Refer to pages 4 - 7
 

Figure 2-9. Meter Operating Ranges Listed on a NTEP Certificate of Conformance 

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b.	 Posting and availability of Operating Ranges 

The operating range of the grain moisture meter shall be clearly and 

conspicuously posted in the place of business such that the information is readily 

visible from a reasonable customer position. The posted information shall 

include the following: ..........................................................................UR.3.10. 

1.	 The temperature range over which the meter can be used and, if the 

temperature range varies for different grains or seed, the range must be 

specified for each. .......................................................................... UR.3.10.(a) 

2.	 The moisture range for each grain or seed for which the meter is to be 

used.. .............................................................................................. UR.3.10.(b) 

3.	 The temperature range for each grain or seed for which the meter is to be used. 

........................................................................................................ UR.3.10.(c) 

4.	 The maximum allowable difference in temperature that may exist between the 

meter and the sample for which an accurate moisture determination can be 

made. .............................................................................................. UR.3.10.(d) 

5.	 Operating instructions are readily available to the user, service technician, and 

weights and measures official to include a list of accessory equipment and the 

kinds of grain or seed to be measured with the moisture meter. ........... UR.3.1. 

Guidance: 

□	 The device owner is responsible for posting the correct ranges of operation for the 

meter. Verify that the ranges specified in NIST Handbook 44, Section 5.56(a), 

S.1.3.(a)-(d) or Part 2, Section 5.2.3. “Operating Ranges and Temperatures” 

items (a) (1- 4) of this manual are posted in the place of business and visible to the 

customer. This information should be in close proximity to the meter so that it is 

readily visible to a customer observing the transaction. 

c.	 Operating Temperature 

1.	 Warm-up Period. When a meter is turned on it shall not display or record any 

usable values until the operating temperature necessary for accurate 

determination has been attained, or the meter shall bear a conspicuous 

statement adjacent to the indication stating that the meter shall be turned on 

for a time period specified by the manufacturer prior to use. ............. S.1.5.(a.) 

2.	 A meter shall meet the requirements of T.2. Tolerances when operated in the 

temperature range of 10 °C to 30 °C (50 °F to 86 °F) or within the range 

specified by the meter manufacturer. .................................................. S.1.5.(b) 

3.	 If the manufacturer specifies a temperature range, the range shall be at least 

20 °C (36 °F). ....................................................................................... S.1.5.(c) 

Guidance: 

□	 The warm-up test is not typically performed in the field since meters are 

usually in use and the temperatures at the test location are within the operating 

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temperatures of the meter. When testing at a location where the meters have 

not been in use for a period of time and the temperature of the location exceeds 

the operating temperature of the meter, the warm-up can be tested by turning 

the meters on and testing the meters with grain sample to verify that usable 

values are not recorded or displayed until the meter reaches its operating 

temperature. 

□	 When testing for meter accuracy within the operating ranges for the meter, the 

meter must meet the tolerances as specified in NIST Handbook 44, 

Section 5.56.(a). 

□	 When looking at the operating ranges for the meter verify the manufactures 

specified temperature range is at least 20 °C (36 °F) 

Electrical Power Supply 

[Code References: NIST Handbook 44, Section 5.56.(a) GMM, S.2.2., S.2.2.1, S.2.2.2] 

a.	 Power Supply, Voltage and Frequency. A meter that operates using alternating 

current must perform within the tolerances defined in 

Section T.2. “Tolerances” over the line voltage range 100 V to 130 V, or 200 V 

to 250 V rms as designed, and over the frequency range of 59.5 Hz to 60.5 Hz. 

Battery-operated instruments shall not indicate or record values outside the 

applicable tolerance limits when battery power output is excessive or deficient. 

............................................................................................................S.2.2.1. 

b.	 Power Interruption. A power interruption shall not cause an indicating or 

recording element to display or record any values outside the applicable 

tolerance limits....................................................................................S.2.2.2. 

Guidance: 

□	 The power supply, voltage and frequency test is not typically conducted in the field 

on electrically powered grain moisture meters because this test requires a source 

to change the voltage and frequency in the power supply. However, the power 

supply, voltage and frequency test may be performed on battery operated 

instruments if it can be determined that the battery power is in excessive or 

deficient and then by verifying that the meter performs in tolerance while the 

battery power is in this condition. 

□	 If interruptions to the power can be made that do not disrupt the normal flow of 

business, such as turning a room switch on and off that controls the power to a 

moisture meter, observations may be made to verify that this interruption does not 

cause an indicating or recording element to display or record any values outside 

the applicable tolerance limit. 

Units and Readability 

[Code References: NIST Handbook 44, Section 5.56.(a) GMM, S.1.4.] 

The display permits moisture value determination to both 0.01 % and 0.1 % 

resolution. The 0.1 % resolution is for commercial transactions; the 0.01 % 

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resolution is for type evaluation and calibration purposes only, not for 

commercial purposes. Test weight per bushel values shall be determined to the 

nearest 0.1 pound per bushel. ....................................................................S.1.4. 

Guidance: 

□	 Meters are allowed to display in two different percent resolutions for moisture. 

The 0.01 % resolution is a finer resolution to allow for rounding during type 

evaluation and calibration of the meter. There is a single resolution for test weight 

per bushel which is 0.1 pounds per bushel. The 0.1 % resolution for moisture and 

the 0.1 pounds per bushel must be used for commercial transactions. Prior to 

accuracy testing, ensure that the meter is indicating in 0.1 % resolution for moisture 

and in 0.1 pounds per bushel for test weight. If the meter is indicating in a different 

resolution record the “as found” resolution on your report form; explain the 

requirement to the device owner; and have the device owner change the resolution 

to the appropriate resolution for field testing following instructions in the operation 

manual. 

Recorded Representation 

[Code References: NIST Handbook 44, Section 5.56.(a) GMM, G-S.5.6., UR.3.4. (a), (b)] 

a.	 Insofar as they are appropriate, the requirements for indicating and recording 

elements shall also apply to recorded representations. All recorded values shall 

be printed digitally. In applications where recorded representations are 

required, the customer may be given the option of not receiving the recorded 

representation. For systems equipped with the capability of issuing an 

electronic receipt, ticket, or other recorded representation, the customer may 

be given the option to receive any required information electronically (e.g., via 

cell phone, computer, etc.) in lieu of or in addition to a hard copy. .....G-S.5.6. 

b.	 Printed tickets must be free from any previous indication of moisture content 

or type of grain or seed selected. The customer shall be given a printed ticket 

showing the date, grain type, grain moisture results, test weight per bushel, and 

calibration version identification. The ticket shall be generated by the grain 

moisture meter system. ..............................................................UR.3.4.(a),(b) 

Guidance: 

□	 Observe transactions to ensure that a printed ticket is given to customers and the 

printed results show all of the information listed in NIST Handbook 44, Section 

5.56.(a), UR.3.4. or in Part 2, Section 5.2.7. “Recorded Representation” of this 

manual. Also verify that the receipt is printed from the grain moisture meter 

system. This may be printed by a printer integral to the grain moisture meter or by 

an external printer interfaced to the meter; the receipt may not be generated by 

manual operation. During accuracy testing print out and review a ticket. 

Provisions for Sealing 

[Code References: NIST Handbook 44, Section 1.10. General Code, G-S.8., G-UR.4.5., 

Section 5.56.(a) GMM, S.2.5., Table S.2.5.] 

a.	 A device shall be designed with provision(s) for applying a security seal that 

must be broken, or for using other approved means of providing security (e.g., 

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data change audit trails available at the time of inspection), before any change 

that detrimentally affects the metrological integrity of the device can be made 

to any electronic mechanism..................................................................G-S.8. 

[Nonretroactive as of January 1, 1990] 

b.	 A security seal shall be appropriately affixed to any adjustment mechanism 

designed to be sealed.......................................................................G-UR.4.5. 

c.	 Provision shall be made for applying a security seal in a manner that requires 

the security seal to be broken, or for using other approved means of providing 

security (e.g., audit trail available at the time of inspection as defined in 

Table S.2.5. “Categories of Device and Methods of Sealing,” NIST 

Handbook 44, Section 5.56.(a) before any change that affects the metrological 

integrity of the device can be made to any mechanism. ...........................S.2.5. 

Guidance: 

□	 If a feature or parameter of the moisture meter can be changed, that will affect the 

measurement of a device, there must be a means for sealing that feature or 

parameter to ensure that there is evidence that a change was made to the device. 

A list of the features and parameters to be sealed are included in Publication 14. 

Acceptable forms of sealing are a physical seal, an event counter or an event 

logger. These types of sealing are applied according to the category of the device. 

Meters are classified as category 1, 2, 3, 3a, and 3b devices: 

o	 If a meter is classified as a Category 1 device, which is a meter that does not 

have remote configuration, the method for sealing can be a physical seal or 

two event counters. 

o	 If a meter is classified as a Category 2 device, which is a device with remote 

configuration but access is controlled by physical hardware, the hardware for 

access to remote communication must have a physical seal or two event 

counters. 

o	 If a meter is classified as a Category 3 device, which is a device with remote 

configuration, a Category 3a, device which is a device with no remote 

configuration but the operator is able to make slope and bias changes or a 

Category 3b device, which is a device with no remote configuration but 

metrological changes can be made through a software switch such as a 

password, these categories require an event logger. 

□	 The NTEP certificate of conformance for a grain moisture meter provides 

information on the type of sealing associated with the meter and includes the 

location of a physical seal or guidelines for accessing event logger and/or event 

counter information. Most NTEP meters are Category 3 devices requiring an audit 

trail (an event logger or event counter). Figure 2-10. “Audit Trail and Key for 

Description of Audit Trail Changes,” contains a printout of an event logger from a 

NTEP grain moisture meter and a key to identify the codes on the event log. 

During testing, review the CC to determine the type of sealing associated with the 

meter being tested then print and review the event logger or event counter to ensure 

that it meets the requirements of NIST Handbook 44, Section 5.56.(a), Table S.2.5. 

“Categories of Device and Methods of Sealing” or observe the physical seal to 

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ensure that the seal is secure and provides adequate security. For meters with event 

loggers or event counters, review the printed event logger or counter for any 

patterns that may indicate inappropriate changes. For example, one pattern that 

may indicate inappropriate changes may be excessive changes during peak harvest 

times. Note on your inspection report whether or not physical seals are intact, note 

settings for any event counters, and attach a copy of the event log if applicable. 

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Figure 2-10. Audit Trail and Key for Description of Audit Trail Changes. 

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Date Time Calibration Constituent Description Change Count 

ID Description of metrological changes ID Description of metrological changes 

1 Import an application model 12 A-constant (residual) (constituent parameter). 

2 Delete an application model. 13 B-constant(leverage) (constituent parameter). 

3 The date setting is changed. 14 Low limit (constituent parameter). 

4 The time setting is changed. 15 High limit (constituent parameter). 

5 The P Constant is changed 16 

C-constant (standard deviation (std dev)) (constituent 

parameter). 

6 The O constant is changed 17 Number of printed decimals (constituent parameter). 

7 The S constant is changed 18 Slope changes (constituent parameter) 

8 The min temperature is changed (constituent parameter) 19 Changes of BIAS (constituent parameter). 

9 The max temperature is changed (constituent parameter) 20 Moisture correction (constituent parameter). 

10 Instrument temperature limit. 21 Correction of constituent (constituent parameter). 

11 Number of subsamples (application model parameter). 22 Make correction (constituent parameter). 

Marking Requirements 

Marking requirements specify what must be marked on the grain moisture meter for proper 

identification of the device and marking requirements for operational controls; graduations; 

indications; and features. 

General Identification 

[Code Reference: NIST Handbook 44, Section 1.10. General Code, G-S.1.(a)-(e)] 

a.	 All equipment, except weights and separate parts necessary to the 

measurement process but not having any metrological effect, shall be clearly 

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and permanently marked for purposes of identification with the following 

information: .............................................................................G-S.1.(a)-(e) 

1.	 the name, initials, or trademark of the manufacturer or distributor;...G-S.1.(a) 

2.	 a model identifier that positively identifies the pattern or design of the 

device;............................................................................................. G.S.1.(b) 

- The model identifier shall be prefaced by the word “Model,” “Type,” 

or “Pattern.” These terms may be followed by the word “Number” or 

an abbreviation of that word. The abbreviation for the word “Number” 

shall, as a minimum, begin with the letter “N” (e.g., No or No.). The 

abbreviation for the word “Model” shall be “Mod” or “Mod.” Prefix 

lettering may be initial capitals, all capitals, or all lower case. 

[Nonretroactive as of January 1, 2003] 

(Added 2000) (Amended 2001) 

3.	 a nonrepetitive serial number, except for equipment with no moving or 

electronic component parts and not-built-for-purpose, software-based 

devices; .......................................................................................... G-S.1.(c) 

[Nonretroactive as of January 1, 1968] 

(Amended 2003) 

- The serial number shall be prefaced by words, an abbreviation, or a 

symbol, that clearly identifies the number as the required serial 

number. 

[Nonretroactive as of January 1, 1986] 

- Abbreviations for the word “Serial” shall, as a minimum, begin with 

the letter “S,” and abbreviations for the word “Number” shall, as a 

minimum, begin with the letter “N” (e.g., S/N, SN, Ser. No., and 

S. No.). 

[Nonretroactive as of January 1, 2001]
 

4.	 the current software version or revision identifier for not-built-for-purpose, 

software-based devices; ................................................................. G-S.1.(d) 

[Nonretroactive as of January 1, 2004] 

(Added 2003) 

- The version or revision identifier shall be prefaced by words, an 

abbreviation, or a symbol, that clearly identifies the number as the 

required version or revision. 

[Nonretroactive as of January 1, 2007] 

(Added 2006) 

- Abbreviations for the word “Version” shall, as a minimum, begin with 

the letter “V” and may be followed by the word “Number.” 

Abbreviations for the word “Revision” shall, as a minimum, begin with 

the letter “R” and may be followed by the word “Number.” The 

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abbreviation for the word “Number” shall, as a minimum, begin with
 

the letter “N” (e.g., No or No.). 

[Nonretroactive as of January 1, 2007]
 

(Added 2006) 

5.	 a National Type Evaluation Program (NTEP) Certificate of Conformance 

(CC) number or a corresponding CC Addendum Number for devices that 

have a CC. The CC Number or a corresponding CC Addendum Number 

shall be prefaced by the terms “NTEP CC,” “CC,” or “Approval.” These 

terms may be followed by the word “Number” or an abbreviation of that 

word. The abbreviation for the word “Number” shall, as a minimum, begin 

with the letter “N” (e.g., No or No.). ............................................. G-S.1.(e) 

[Nonretroactive as of January 1, 2003] 

Guidance: 

□	 Meters must be marked in accordance with NIST Handbook 44, Section 1.10. 

General Code, G.S.1.(a)-(e). Much of the marking information required by GS.1. is often found on an identification badge. However, the information is not 

required to be marked on a badge and may be located at various places on the 

device, provided it complies with visibility and permanence requirements. 

Devices must be marked with the appropriate information to ensure that each 

device is uniquely identified so that proper records and inspection trails can be 

maintained by weights and measures jurisdictions and service agencies. 

Appropriate markings are also necessary to track devices that may have been 

sold or transferred to different business locations in or out of jurisdictions. 

Prior to testing locate the identification information on the meter. Confirm that 

identification of the meter includes all the requirements included in NIST 

Handbook 44, Section 1.10. General Code, G.S.1.(a)-(e) and record the 

necessary information on the test report. Figure 2-11. “Examples of pre 2003 

Identification Badge” shows a sample identification badge. In this sample, the 

ID badge does not include a CC number. Although this ID badge does not 

include a CC number, it meets the requirements of NIST Handbook 44 because 

it was manufactured prior to January 1, 2003. The requirement for including a 

CC number only applies to meters manufactured after January 1, 2003. The 

NTEP CC includes information on where to locate the identification badge and 

identification information that can be assessed from the instrument display. 

Figure 2-11. Example of pre 2003 Identification 

Badge. (Note: The ID badge does not include a CC 

number.) 

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Interchange or Reversal of Parts 

a.	 Parts of a device that may readily be interchanged or reversed in the course of 

field assembly or of normal usage shall be:........................G-S.4.(a),G-S.4.(b) 

1.	 so constructed that their interchange or reversal will not affect the performance 

of the device; or 

2.	 so marked as to show their proper positions. 

Guidance: 

□	 During an inspection of any new meter designs with interchangeable or 

reversible parts, testing should be performed to ensure that these parts are 

marked appropriately and if not marked they do not affect the performance. If 

the part is not properly marked to show its proper position, a test can be 

performed by first testing the meter with the part attached in one direction then 

reattaching the part in another direction to determine if the reversal of the part 

affected the performance of the device. This is to ensure that reversing a part 

does not cause inaccurate measurements. Current designs of NTEP grain 

moisture meters do not have parts that can be readily interchanged during 

normal use. As with other Handbook 44 requirements, compliance with these 

requirements is verified during type evaluation. 

Marking, Operational Controls, Indications and Features 

a.	 All operational controls, indications, and features, including switches, lights, 

displays, push buttons, and other means, shall be clearly and definitely 

identified. The use of approved pictograms or symbols shall be acceptable. 

............................................................................................................G-S.6. 

[Nonretroactive as of January 1, 1977] 

Guidance: 

□	 Review the identification of operational controls, indications, switches, light 

displays, and push buttons to ensure that they are clearly identified. These 

requirements help to ensure that device owners can operate the device 

appropriately and ensures consumers can understand the transaction and 

information displayed and recorded. This identification may include 

pictograms or symbols that have been approved by the weights and measures 

community and that would be readily understood by an operator or consumer. 

Information on identification of the operational controls is typically located in 

the manufacturer’s operations manual. Figure 2-12. “Identified Operational 

Controls” below shows the identification of operational controls on one NTEP 

meter. 

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Figure 2-12. Identified 

Operational Controls. 

Values 

If graduations, indications, or recorded representations are intended to have 

specific values, these shall be adequately defined by a sufficient number of 

figures, words, symbols, or combinations thereof, uniformly placed with 

reference to the graduations, indications, or recorded representations and as close 

thereto as practicable, but not so positioned as to interfere with the accuracy of 

reading. .............................................................................................G-S.5.2.4. 

Guidance: 

□	 Grain moisture meters and multi-constituent meters measure moisture and/or 

protein, starch, and oil of grains in percent (%) value and grain test weight in 

pound per bushel (lb/bu) or Kilogram per hectoliter (kg/hl). Abbreviations for 

grain type may also be used in accordance with NIST Handbook 44, Section 

5.56.(a), Table S.1.2. “Grain Types and Multi-Class Groups Considered for 

Type Evaluation and Calibration and Their Minimum Acceptable 

Abbreviations.” Observations should be made while testing to ensure that the 

constituents are properly labeled; that minimum acceptable abbreviations are 

used for the various grain types; and that the measurement values are identified 

appropriately. 

Permanence 

Graduations, indications, or recorded representations and their defining figures, 

words, and symbols shall be of such character that they will not tend easily to 

become obliterated or illegible. ..........................................................G-S.5.2.5. 

On Devices that Indicate or Record in more than One Unit 

On devices designed to indicate or record in more than one unit of measurement, 

the values indicated and recorded shall be identified with an appropriate word, 

symbol, or abbreviation. ....................................................................G-S.5.3.1. 

Lettering 

All required markings and instructions shall be distinct and easily readable and 

shall be of such character that they will not tend to become obliterated or 

illegible. ..................................................................................................G-S.7. 

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Other Devices not used for Commercial Measurements 

If there are other moisture meters on the premises not used for trade or 

determining other charges for services, these devices shall be clearly and 

conspicuously marked “Not for Use in Trade or Commerce.” 

..............................................................................................................UR.3.2. 

Guidance: 

□	 Examine the markings on all meters on the premises. For those not used 

commercially ensure that they are marked “Not for Use in Trade. For all others 

observe that: 

o symbols, words and figures are not easily obliterated; 

o different units are properly identified; and 

o marking and instruction are easily read. 

Measuring Element 

Accessory Devices/Equipment 

When the operating instructions for a moisture meter require accessory 

equipment separate from and external to the moisture meter, such equipment 

shall be appropriate and complete for the measurement and Accessory devices, 

if necessary in the determination of a moisture content value, shall be in close 

proximity to the moisture meter and allow immediate use. .............S.3., UR.3.5. 

Current Calibration Data 

a.	 Grain moisture determinations must be made using only the most recently 

published calibration data. .................................................................UR.3.9. 

b.	 A meter must be capable of displaying either calibration constants, a unique 

calibration name, or a unique calibration version number for use in verifying 

that the latest version of the calibration is being used to make moisture content 

and test weight per bushel determinations. .........................................S.2.4.1. 

Guidance: 

□	 Grain moisture meter calibrations are based on how the meter reacts to grain 

samples, which vary with each crop year. As such, the calibrations of grain 

moisture meter may change on an annual basis. Meter manufacturers provide 

meter owners with the most current calibrations annually. Device owners are 

responsible for ensuring that the latest calibrations are installed on the meter. 

Calibration constants, unique calibration name, or calibration versions numbers 

for grain moisture meters are listed on the NTEP CC. An example of the 

calibrations and calibration version number on a CC are shown in 

Figure 2-13. “Calibrations Data from a GMM Certificate of Conformance.” 

Compare the meter calibrations, unique calibration name or calibration version 

on the meter to the values on the most current CC to verify that the most recent 

calibrations are installed on the meter. 

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Hard Red Winter Wheat 

Designation: Wheat HRW 

Calibration Version: 060308n 

Moisture Range - Approved: 6 % – 20 % 

Moisture Range - Pending: 6 % – 22 % 

Calibration Constants: 

K1 = 0673 K4 = 0738 K7 = 2206 

K2 = 1716 K5 = 2500 K8 = 9948 

K3 = 1247 K6 = 1074 K9 = 1045 

Test Weight per bushel: Approved 

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Figure 2-13. Calibration Data from a GMM Certificate of Conformance. 

Pretest Determinations 

Grains and Constituents 

Determine the kind of grains, and constituents the device is used to measure and select the 

grains for use in inspecting and testing the meter. 

Tolerances 

[Code References: NIST Handbook 44, Section 5.56.(a) GMM, T.1., T.2., T.3.] 

How to Apply Tolerances 

a.	 Tolerances shall be applied to the average of at least three measurements on 

each official grain sample for moisture and weight per bushel measurements) 

b.	 The tolerances hereinafter prescribed shall be applied to errors of 

underregistration and errors of overregistration. ...................................... T.1. 

c.	 Air Oven Reference Method. – Maintenance and acceptance tolerances shall 

be as shown in Table T.2.1. “Acceptance and Maintenance Tolerances AirOven Reference Method.” Tolerances are expressed as a fraction of the 

percent moisture content of the official grain sample, together with a minimum 

tolerance. ..................................................................................... T.2., T.2.1. 

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Table T.2.1. 

Acceptance and Maintenance Tolerances Air-Oven Reference Methods 

Type of Grain, Class, or Seed Tolerance Minimum Tolerance 

Corn, oats, rice, sorghum, 

sunflowers 

0.05 of the percent 

moisture content 

0.8 % 

in moisture content 

All other cereal grains an doil 

seeds 

0.04 of the percent 

moisture content 

0.7 % 

in moisture content 

(Amended 2001) 

d.	 The maintenance and acceptance tolerances on test weight per bushel 

indications or recorded representations are shown in Table T.3. “Acceptance 

and Maintenance Tolerances Test Weight per Bushel.” ........................... T.3. 

Table T.3. 

Acceptance and Maintenance Tolerances Test Weight per Bushel 

Type of Grain or Seed Tolerance 

(Pounds Per Bushel) 

Corn, oats 0.8 

All wheat classes 0.5 

Soybeans, all barley classes, all rice 

classes, sunflower, sorghum 0.7 

(Added 2003) 

Guidance: 

□	 The following is an example of calculating the tolerance for a wheat sample: 

Per Table T.2.1. “Acceptance and Maintenance Tolerances Air-Oven 

Reference Methods,” the tolerance for wheat is 0.04 of the percent moisture 

content of the standard grain sample, with a minimum tolerance of ± 0.7 %. If 

the wheat sample moisture is 16 %, the tolerance is calculated by multiplying 

the tolerance by the percent moisture: 

± 0.04 × 16 % = 0.64 % 

So the tolerance to be applied to this test is ± 0.64 %. However, since the 

minimum tolerance to be applied is ± 0.7 %, the tolerance for the test is 

± 0.7 %. 

□	 The tolerances for test weight measurements are applied directly to the 

measurement. The sample used for test weight has a test weight value assigned 

by the laboratory. The sample is placed in the meter and the test weight 

indicated by the meter is compared to the laboratory assigned test weight values 

of the sample. 

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Test Notes 

Official Grain Sample Maintenance, Test Methods and Documentation 

The moisture of official grain samples will change over time due to temperature, 

environmental conditions, and stability of the grain samples. To maximize the use of the 

official grain example and ensure that the moisture value of the sample is maintained 

throughout testing, field inspectors must follow guidelines and test procedures included in 

this section. The test methods and documentation needed to perform inspection and testing 

are also included in this section. 

Storage 

Official grain samples received from the laboratory are to be stored in a 

refrigerator and maintained at 2 oC (35 °F) to 4 oC (40 °F) until needed. 

Official Grain Samples used for Field Testing 

Official grain samples for field testing are grains that are representative of the 

grain types and moisture ranges normally traded in a jurisdiction. Three or more 

official grain samples with a high moisture content and three or more official 

grain samples with a low moisture content for each grain type are used for field 

testing commercial grain moisture meters. One of the three or more official grain 

samples is retained as a backup for each grain type and moisture. Each of the 

remaining samples is used as an official sample until it has been dropped for the 

number of times described in Part 2, Section 7.1.4. “Minimum Test and 

Maximum Number of Drops” of this manual. 

Warming Official Grain Samples in Preparation for Testing 

Approximately two hours before use (consider travel time in this two-hour 

period), remove only the official grain standards from the refrigerator that will 

be used for moisture meter field evaluation for that day of testing and shake the 

sample several times (for homogeneity). Place the samples in a transport cooler 

WITHOUT ICE. This will allow the grain sample to stabilize to ambient 

temperature and minimize exposure to temperature extremes and fluctuations. 

The sample jars or bags should be spread out to allow the air to move freely 

about them. Official grain samples which are being used to test moisture meters 

for the current day should be stored in the transport cooler when not in use. If 

there are significant down times between tests during the day, grain standards 

should be stored in the refrigerator until two hours before they are needed. Backup samples must remain in the portable refrigerator until needed by the inspector. 

When it is determined that the back-up sample is needed that day, the back-up 

sample should be placed in the cooler along with the day’s primary samples. 

Note: Throughout the handling period when the grain is not refrigerated, 

occasionally shake each grain sample to mix the grain several times and also be 

sure to shake the grain sample before removing the sealing lid for any purpose. 

Minimum Test and Maximum Number of Drops 

a.	 A minimum test of a grain moisture meter consists of testing the moisture and if 

applicable, test weight meter measurements. 

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b.	 When testing for moisture, the meter is to be tested using official grain samples 

having at least two different moisture content values (“high” and “low” moisture 

content) within the operating range of the device and representing the “high” and 

“low” moisture values at which a specific grain is traded within a jurisdiction. 

c.	 When applicable, the test weight feature on the meter should be tested using an 

official grain sample with the lowest moisture value. 

d.	 The moisture value of grain samples may begin to change in moisture during 

meter testing. High moisture corn and soybeans and other grains and moistures 

have a maximum number of drops during testing. High moisture corn and 

soybeans and rough rice standard samples can be used for a maximum number 

of 18 drops. Corn and soybeans below 18 % and all other grains and moistures 

have a maximum number of 24 drops. Extended use of grains for more than the 

specified maximum number of drops must be supported by data to show that 

testing is not affected by the extended use of the grain samples. 

Preparation of the Official Grain Samples upon Arrival at the Test Site 

a. Upon arrival at the test site, transport the official grain samples to the meter 

location in the transport cooler. The grain samples should be taken into the room 

where the moisture meter is located; taken out of the transport cooler; and placed 

near the moisture meter to allow them to reach the temperature of the room 

before the jar is opened. Jars should not be opened until the grain is within 

10 degrees of the room temperature. Moisture will condense on the grain if a 

cold grain standard is opened before its temperature stabilizes. Except when 

inserting a thermometer to take the temperature of the grain, the jar containing 

the official grain sample is never opened without first allowing the grain to 

stabilize and is only exposed while conducting the moisture meter test. 

b. Take the temperature of the grain sample with the least amount of exposure to 

the environment. One method is to quickly replace the lid on the sample with a 

rubber stopper or lid with a hole that allows a thermometer to be inserted into 

the sample. 

c. In order to ensure a valid result, care must be taken so that the moisture values 

of the samples are carefully maintained. High moisture samples are more 

susceptible to moisture loss and spoilage; therefore, it is recommended that the 

inspection begin with the sample having the highest moisture value and proceed 

to the samples with the lower moisture values to limit the amount of time that 

the high moisture samples are exposed to ambient conditions. 

d. Work with only one sample at a time to avoid the possibility of confusing/mixing 

the samples. 

e. Carefully monitor each sample in order to detect any erratic meter readings or 

foul odor which could indicate sample deterioration. 

f. To avoid contamination of the official samples, the meter, its parts, and 

accessory equipment must be clear of other grain before using the official grain 

samples in the meter. Prior to using an official grain sample in a GMM under 

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test, check to ensure that the GMM dump cells, filling hoppers, grain drawers 

(receiving trays), etc. are clean and there is no buildup of residue. 

g.	 Before opening the sample to begin testing the GMM, review all the details of 

the inspection so that handling of the grain and the time the sample is out of the 

sealed container can be minimized. 

h.	 Field inspectors are responsible for refrigerating samples at the end of each day 

and for keeping samples in a cooler or refrigerator between inspection points. 

Inspectors are also responsible for monitoring sample conditions and possible 

moisture changes to determine when replacement is necessary. This includes 

keeping the sample free of contamination from other grains, souring or molding 

grain, and insects, all of which may cause erratic readings. A primary grain 

sample that begins to fail on all meters may be indicative of a moisture change 

in the primary grain sample. If a primary sample is compromised as noted above, 

the back-up sample should be used to confirm the readings. If meters pass with 

the back-up sample, place the previously used official grain sample in the 

refrigerator for return to the laboratory, and use the back-up grain sample to 

complete the testing. 

Field Inspection and Test Method 

Field inspection of NTEP grain moisture meters or meters manufactured or 

placed into service after January 1, 1998, must be conducted in accordance with 

NIST Handbook 44, Section 5.56.(a). This manual provides guidelines for using 

the air-oven reference method transfer standards to test GMM and multiconstituent grain analyzers that measure moisture in accordance with NIST 

Handbook 44, Section 5.56.(a), N.1.1. 

Documentation 

In addition to NIST Handbook 44, other documents are needed and useful in 

performing the inspection of GMMs. These documents provide information on 

jurisdictional policy, device operation, accessing audit trail information, 

verifying NTEP identification information, and the location of businesses with 

grain moisture meters. 

a.	 Departmental Policy and Inspection Procedures 

Many weights and measures jurisdictions have state and/or local policies 

and inspection procedures that are followed during an inspection. These 

procedures should be provided to the inspector for reference. 

b.	 Moisture Meter Operating Instructions and Current Certificates of 

Conformance (CC) for Moisture Meters 

GMM operating instructions from the manufacturer will provide the 

inspector with detailed information on how to operate the meter and will 

be useful to the inspector if the meter is new or if it is the first time an 

inspector has tested a specific type of meter. CCs are available for all 

NTEP GMMs and may be obtained from the NCWM, Inc. website at 

www.ncwm.net. A CC for grain moisture meters includes the most current 

calibration constants, sealing requirements, and other useful information 

that the inspector will need to perform an inspection. 

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c.	 List of Moisture Meters and Locations, Type of Meters(s), and Types(s) 

of Grain Purchased 

Many weights and measures jurisdictions maintain a database or other 

listing of moisture meters with the location, type of meters, and grains 

purchased. This information will be helpful for the inspectors to prepare 

for testing. 

Official Grain Samples (Transfer Standards), Minimum Test, Minimum 

Sample Size. 

[Code References: NIST Handbook 44, Section 5.56.(a) GMM, N.1.1., N.1.2., UR.3.3., 

S.2.1.] 

a.	 Official grain samples shall be used as the official transfer standards with moisture 

content and test weight per bushel values assigned by the reference methods. The 

reference methods for moisture shall be the oven drying methods as specified by the 

USDA GIPSA. The test weight per bushel value assigned to a test weight transfer 

standard shall be the average of 10 test weight per bushel determinations using the 

quart kettle test weight per bushel apparatus as specified by the USDA GIPSA. 

Tolerances shall be applied to the average of at least three measurements on each 

official grain sample. Official grain samples shall be clean and naturally moist, but 

not tempered (i.e., water not added). ............................................................. N.1.1. 

b.	 A means to prevent condensation of moisture or loss of moisture from grain 

samples must be used. For example, a cold grain sample should be kept in a closed 

container in order to permit the cold grain to come to within the operating 

temperature range of the meter before the grain moisture measurements are 

made. ........................................................................................................UR.3.3. 

c.	 Meters shall be designed to measure the moisture content of representative-size 

grain samples. The minimum allowable sample size used in analysis shall be 100 g 

or 400 kernels or seeds, whichever is smaller................................................S.2.1. 

d.	 A minimum test of a grain moisture meter consists of test with samples (need not 

exceed three) of each grain or seed for which the device is used and for each grain 

or seed type shall include the following: ..................................................... N.1.2. 

- tests of moisture indications, using samples having at least two different moisture 

content values within the operating range of the device. ........................... N.1.2.(a) 

- if applicable, tests of test weight per bushel indications with at least the lowest 

moisture samples used in (a) above. .......................................................... N.1.2.(b) 

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Safety Reminders 

Lifting. 

• Be familiar with and use proper lifting techniques when lifting grain samples or heavy 

equipment to prevent personal injury. 

o To reduce the possibility of back injury, use equipment which would decrease the 

amount of lifting required whenever possible (e.g., an extended height funnel, or 

carts for transporting grain samples) 

o Periodic training in proper lifting techniques is encouraged. 

Grain Sample Container. 

• Use a lid opener if a grain sample container lid is too tight to be removed comfortably by 

hand. Do not strain. When opening samples, grasp the containers firmly with good hand 

and wrist positioning and grip. 

• Dry condensation from the outside of a grain sample container to prevent slippage and 

possible breakage of container and/or injury to feet. 

• Watch for chips, cracks, or breakage of glass containers. If found, dispose of the container 

properly to prevent injury to the inspector or damage to the GMM. A damaged container 

may also affect the integrity of the grain sample moisture. 

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Test 

Minimum Test 

Carefully review Section 7.1. “Official Grain Sample Maintenance, Test Methods and 

Documentation,” before beginning the minimum test procedures and follow the guidelines 

in this section. 

a.	 Determine the official grain sample temperature and the ambient temperature. Do not 

remove the grain from the container until the grain is within 10 °F of the ambient 

temperature. 

b.	 When the grain comes to within the desired temperature, pour the entire contents of the 

official grain sample into a larger, clean glass container. Rotate the container about 

10 times to further homogenize the contents and equilibrate the temperature. 

c.	 Following the GMM operating instructions, select the grain type to be tested on the 

GMM. 

d.	 Fill the grain hopper with the official grain sample, starting with the high moisture 

sample first. 

e.	 Following the GMM operating instructions drop the official grain sample through the 

meter and record the moisture results. Repeat the test for a total of three measurements. 

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f. If there are other GMMs at the inspection site, repeat steps (a.) through (e.) with the same 

official grain sample, working in assembly-line fashion as quickly as possible. 

g. Return the official grain sample to its original, clean jar; seal the jar with its lid; mark the 

jar with the number of drops; and return the jar to the cooler. 

h. Analyze the test results by averaging the three-meter moisture measurements for each 

meter and comparing the average meter moisture to the known moisture value of the 

official grain sample and record the error. 

i. If the meter is not in tolerance and you suspect that the sample has changed, is damaged, 

or contaminated, repeat steps (a.) through (h.) with the back-up sample. If the results 

from the back-up sample agree with the results from the primary sample, record the 

results; return the back-up sample to the cooler; and continue to use the primary sample 

as the standard. 

j. Proceed to the next lower moisture level of that grain and repeat steps (a.) through (h.) 

k. If the results from the back-up sample are different, return the primary sample to the 

portable refrigerator for return to the laboratory. Use the back-up sample as the primary 

from this point. 

l. Repeat steps (a.) through (h.) for each grain and each moisture level. 

m. If appropriate, test the test weight per volume (e.g., test weight per bushel) indications 

with at least the lowest moisture sample. Drop the official grain sample with the lowest 

moisture through the meter three times and record the results. Analyze the test results 

by averaging the three-meter test weight measurements for each meter and comparing 

the average meter test weight to the known test weight value of the official grain sample 

and record the error. Evaluation of the test weight per bushel indications can be 

performed while testing the moisture indications or a weights and measures jurisdiction 

may choose to use a separate, low-moisture sample to test the accuracy of the test weight 

indications. 

n. Remember to mark each sample label with the number of times that sample is dropped 

and the number of times that sample was warmed. 

o. Verify that the seals of the jars are tight and return the samples to the portable refrigerator 

as soon as testing is completed for the day. 

p. When samples exceed a specified number of drops, 18 drops for corn and soybeans above 

18 % or 24 drops for all other grain types, the sample must be returned to the laboratory 

and retested. A jurisdiction may determine that the maximum number of drops can be 

increased with supporting historical data. 

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Part 2: Field Inspection and Evaluation 

Post Test Tasks 

Provisions for Sealing 

[Code References: NIST Handbook 44, Section 5.56.(a) GMM, S.2.5.] 

Provision shall be made for applying a security seal in a manner that requires the security 

seal to be broken, or for using other approved means of providing security (e.g., audit trail 

available at the time of inspection as defined in Table S.2.5. “Categories of Device and 

Methods of Sealing,” NIST Handbook 44, Section 5.56.(a) before any change that affects 

the metrological integrity of the device can be made to any mechanism. ................... S.2.5. 

Guidance: 

As appropriate, follow the instructions for accessing audit trail information in the NTEP 

certificate “Field Inspection Notes” and review the audit trail of the GMM device for 

compliance with NIST Handbook 44. As appropriate, check for the presence of a physical 

security seal on the meter. Document missing physical seals on the official report and 

apply new ones as needed. Attach a copy of the printed event logger or event counter to 

the test report and record any concerns on the test report. 

Record Results 

Record the test results on an official test report. See Appendix A for a sample test report. 

A test report form for grain moisture meters should contain as a minimum: 

a. name or initials of person performing the evaluation; 

b. date; 

c. description of the device, model, and serial number; 

d. environmental readings such as temperature, where applicable; 

e. identification of standard grain samples (i.e., sample ID); 

f. device owner, name, address and phone number; 

g. device CC number; 

Safety Reminders 

•	 Be sure all equipment being transported by the inspector or service technician is properly 

secured in the vehicle. 

•	 Practice defensive driving when traveling between sites. 

h.	 field evaluation data; 

i.	 calculations; 

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j. numerical checks on calculation; 

k. sealing/audit trail information; and 

l. additional information such as device condition and other comments. 

Review Results 

a. Test Data 

The test data are to be entered in the appropriate spaces on the report form 

during and immediately following the test. 

b. Reporting Error 

To report the error of the meter under test, the moisture value of the grain 

standard is subtracted from the average of three readings of the meter that is 

being tested 

Error = Average meter reading − Grain Standard Moisture Value 

c. Explain Results to Device Owner 

Explain the results to the device owner including any corrective action needed 

and the disposition of the device 

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Appendix A. Grain Moisture Meter Test Report 

Grain Moisture Meter Examination Report 

Firm 

Name: ________________________________________________ Telephone: ____________________________________ Report Number: __________________________ Page _________of__________ 

Address: 

_______________________________________________________ Company representative: __________________________ Date:_____________________ Date of last inspection:_____________________ 

City/Town: _____________________________________________ Zip: 

_______________ Title:__________________________________________ 

Inspector:____________________________________ Time In: _____________ 

Time 

out:_____________ 

Meter Description ____________________________________________________________________ Manufacturer ____________________________________________ User ID_______________________________ 

Model _______________________________________ Serial Number_______________________ NTEP CC number ________________________________________ 

Printer: _______________________________ Calibration Version_______________________________________ Audit Trail Information Printed and Attached Y_____ N_____ 

I acknowledge receipt of this report and certify that I understand the information and/or instructions described herein. Signature for firm: _____________________________________________________________ 

Grain 

Standard 

Air 

temp 

° C 

Grain 

temp 

° C 

Meter 

% Moisture 

Indications 

Avg. 

Meter % 

Moisture 

Grain 

Standard 

% Moisture 

Value 

Moisture Error = 

(Average Meter % 

Moisture - Standard % 

Moisture) 

Meter 

Weight Per 

Bushel 

Indications 

Average Meter 

Weight Per 

Bushel (Test 

Weight) 

Indications 

Grain Standard 

Weight Per 

Bushel 

(Test Weight) 

Wt. Per Bushel 

(Test Weight) 

Error = 

(Avg. Meter Wt. 

Per Bushel − Std. 

Wt. Per Bushel 

Drop 1Drop 2Drop 3Drop 1Drop 2Drop 3 

Type: 

I.D: 

Type: 

I.D: 

Type: 

I.D: 

Type: 

I.D: 

Type: 

I.D: 

Type: 

I.D: 

APPENDIX A. Grain Moisture Meter Sample Test Report Form
 

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Appendix A. Grain Moisture Meter Test Report 

Grain Moisture Meter Examination Report 

Firm 

Name: ________________________________________________ Telephone: ____________________________________ Report Number: __________________________ Page _________of__________ 

Type: 

I.D: 

Type 

I.D: 

Type: 

I.D: 

Type: 

I.D: 

This device has been examined for compliance with the specifications, tolerances, and technical requirements set forth in the latest edition of the National Institute of Standards and Technology Handbook 44 and the 

______________________ weights and measures law. 

Action Taken:  approved,  rejected,  condemned. Any violations must be corrected by ___________________________. 

Violations: Accessory equipment: 

Remarks/Instructions: 

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Appendix B. 

Grain Moisture Air-Oven Reference Methods in the United States1 

Byline: G. Diane Lee 

Grain moisture air-oven reference methods are used by many stakeholders in the United States and these 

reference methods play an important role in measurement accuracy and uniformity of commercial grain 

moisture meter measurements in the country. This article will provide a basic description of the air-oven 

reference methods and their use; discuss the importance of grain moisture measurements in legal-for-trade 

applications; identify the key users of the air-oven reference methods for commercial use; review the origins 

of these air-oven reference methods; and outline the specific air-oven reference methods used for the major 

U.S. grains. 

What are the grain moisture air-oven reference methods in the United States and how are they used? 

The grain moisture air-oven reference methods are procedures used to determine the percent moisture content in grain. 

Basically, a small sample of grain (ground or unground) that represents a larger sample set of that grain is placed in a 

small metal dish and the weight of the sample is recorded. The sample is then placed in an oven at a specific 

temperature and heated for a specific amount of time. The sample is removed from the oven and cooled in a container 

that prevents loss or gain of moisture during the cooling process. Then the sample is reweighed. The loss in the 

sample mass is calculated as the percent moisture content of the grain. 

Commercial grain moisture meters are devices that provide a rapid prediction of moisture in grain and are used to test 

the moisture of grains that are bought and sold in the United States. Calibrations for commercial grain moisture meters 

are developed by comparing the grain moisture meter reading to grain moisture air-oven reference values. Also, airoven reference methods determine the reference moisture values of grain samples that verify the accuracy and 

operation of commercial grain moisture meters. 

Why are grain moisture measurements important in commercial (legal-for-trade) applications? 

Moisture is a critical commercial measurement in grain because “discounts” to the price per bushel of grain are made 

at the time of sale, based on the moisture content of the grain. “Discounts” are reductions to the price per bushel of 

grain. Two examples of discounts are drying and shrinkage discounts. A grain buyer must dry grain that is too high 

in moisture to prevent molding during storage. The cost associated with drying the grain or a “drying discount” is 

determined based on the grain moisture measurement at the time of sale. This discount reduces the amount of money 

the seller receives for the grain. For example, a buyer may be purchasing corn from a seller at $4.00 per bushel of 

corn at a target or desired 15 % moisture content. If the seller’s corn is higher in moisture content at the time of sale 

than is targeted or desired, the buyer will reduce the unit price per bushel he will give the seller for the grain. Grains 

that are too high in moisture may be placed into storage with aeration causing shrinkage. The cost associated with 

shrinkage or a “shrinkage discount” is also based on the moisture of the grain at the time of sale. Errors in the moisture 

measurements may result in large losses to either the seller or buyer of grain. See article number C-006, March 2007 

“The Economic Impact of Errors in Moisture Measurements, Part 2, Grain Moisture Meter Series,” located at: 

www.nist.gov/pml/wmd/pubs/archives-grain-moisture.cfm, for additional information on discounts. 

Who uses air-oven reference methods? 

Stakeholders in the United States that use air-oven reference methods as the basis for commercial measurements of 

moisture in grain include: 

1 Source: Weights and Measures Connection, Volume 3, Issue 6, November 19, 2012. 

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The U.S. Department of Agriculture, Grain Inspection, Packers, and Stockyards Administration (USDA, GIPSA); 

• The National Type Evaluation Program (NTEP) Laboratory for Grain Moisture Meters; 

• Grain Moisture Meter (GMM) Manufacturers; and 

• State Weights and Measures and other state officials. 

These organizations work together to ensure equity in the commercial grain market as illustrated in Figure 1. The 

System of Commercial Grain Moisture Measurements in the United States, and Figure 2., The Movement of Grain in 

The United States and Inspection Points. 

The USDA, GIPSA uses air-oven reference methods to develop the calibrations for the official grain moisture 

meter(s). These official grain moisture meters are used to measure the moisture of grains at export locations and upon 

request at interior grain facilities in the United States. 

The National Type Evaluation Program (NTEP) Laboratory at the USDA, GIPSA uses these air-oven reference 

methods when analyzing a national grain sample set and providing manufacturers with data to develop the calibrations 

for all grain moisture meters used in commercial service in the United States. These reference methods are also used 

to evaluate commercial (i.e., legal for trade) grain moisture meters in the NTEP laboratory to determine if prototypes 

of the device meet the requirements of the National Institute of Standards and Technology (NIST) Handbook 44 

Specifications, Tolerances, and Other Technical Requirements for Weighing and Measuring Devices, prior to being 

used commercially in the United States. See Figure 1., the system of commercial grain moisture measurements in the 

United States. 

State Weights and Measures Officials and other State Officials use these reference methods to determine the moisture 

in grain samples that are used to test commercial grain moisture meters. Typically, the grain moisture meters tested 

by State Weights and Measures or other state officials are at local elevators that purchase grain from farmers in their 

jurisdictions. See Figure 1., the system of commercial grain moisture measurements in the United States and Figure 2., 

the movement of grain in the United States and inspection points. 

Manufacturers of grain moisture meters use these reference air-oven moisture methods when developing the 

calibrations for grain moisture meters that they sell for use in legal-for-trade applications. (See Figure 1. The system 

of commercial grain moisture measurements in the United States.) 

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USDA 

GIPSA 

Air-Oven 

Moistures 

Manufacturers 

Air-Oven 

Moistures 

States AirOven 

Moistures 

NTEP Lab

 Meters 

GIPSA 

Master 

Meter 

Manufacturer's 

Laboratory 

Standard Meters 

Manufacturers 

Production 

Master Meters 

Meters to be 

Shipped 

(These Become 

Field Meters) 

GIPSA Field 

Meter 

GIPSA Field 

Meter 

GIPSA Field 

Meter 

Field Meter 

Field Meter 

Field Meter 

Industry Expectation 

Official System State Weights and 

Measures System 

NTEP and Manufacturing 

System 

Figure 1. The System of Commercial Grain Moisture Measurements in the United States. 

Farm 

Local Elevator 

Terminal 

Elevator 

(Grain May be 

exported from this 

location) 

Export 

Elevators 

Via Trucks 

Usually Via Railway, 

Barges or Ships) 

State Weights and Measures Field Inspection 

Test of commercial meters, typically at local elevators. 

Usually Via Railway, 

Barges or Ships) 

GIPSA Official Inspections 

The official meter is used to test grain 

moisture at Interior facilities and at export 

locations. 

Figure 2. The Movement of Grain in the United States and Inspection Points. 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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Appendix B. Grain Moisture Air-Oven Reference Methods in the United States 

History of Air-oven Reference Methods in the United States 

The most widely recognized reference methods for determining moisture content in grain are based on drying known 

weights of grain in various types of ovens and calculating moisture content from the weight lost in the drying 

operation.2 The USDA, GIPSA, identifies the “air-oven methods” as its official reference methods for determining 

moisture in grain and oil seeds. According to the history of changes to USDA, GIPSA grain standards, these air-oven 

reference methods have been in use since July 1, 1935. The USDA, GIPSA air-oven reference methods were accepted 

by the American Association of Cereal Chemists (AACC, currently known as AACC International), Method 44-15A. 

Although oven methods are subject to error due to the loss of substances other than water during the drying process, 

Hart and Neustadt adapted the use of Karl Fisher (KF) Titration in 1957 to test the accuracy of the USDA air-oven 

moisture methods.i The USDA air-oven methods were designed to give results which agree with those obtained by 

KF Titration. KF Titration provides moisture values by extracting water from grain with the use of a solvent, such as 

methanol, and is more specific for grain moisture. Historical records have noted that KF Titration required more time 

for testing than was practical and, due to the test process at that time, there were repeatability issues from operator to 

operator due to portions of the test that were not automated. Frank E. Jones and Carroll S. Brickenkamp, National 

Bureau of Standards (NBS, now known as the National Institute of Standards and Technology), National Engineering 

Laboratory, noted that techniques were developed to automate KF Titration to address some of the earlier 

disadvantages of this method. Jones and Brickenkamp also noted that, although the KF Titration is more specific for 

moisture, additional tests are needed to determine if other substances react with the solvent used to extract water.3 

The air-oven reference methods remains the reference methods for moisture in the United States; this is likely because 

these methods have been compared to KF Titration and/or other more definitive tests and have proven to provide very 

repeatable measurements. 

Air-oven Reference Methods for Major U.S. Grains 

There are currently eight air-oven moisture reference methods used to determine moisture in the major U.S. grains 

and these methods are recognized internationally. These reference methods vary per grain type, moisture, and 

commodity and are maintained at the USDA, GIPSA in the Technology and Science Division’s Laboratory Work 

Instructions. These work instructions include specific procedures, guidance on test sample size, equipment and 

material, and acceptance criteria needed for each test. Because these air-oven reference methods vary per grain type, 

the following tables are provided to summarize the different air-oven reference methods used in the United States. 

AO_1 

Single-Stage Air-Oven Reference Method for Moisture in Grains, Oilseeds, and Commodities: is the 

difference in weight after drying a ground sample of grain for one hour at 130 oC ± 1 oC (drying time 

is two hours for soybean meal). The following grains and commodities are tested using this method: 

Grains and Oilseeds Commodities 

Description 

Moisture 

Restriction Description 

Barley ≤ 16 % Barley - submitted 

Lentils ≤ 16 % Bulgur 

Oats ≤ 16 % Corn Soy Blend 

Pea ≤ 16 % Corn Soya Flour 

Rice, brown ≤ 16 % Corn Soy Milk 

Rice, milled ≤ 16 % Corn - submitted 

Rice, rough ≤ 13 % Corn Meal 

Rye ≤ 16 % Dessert Powder 

2 Storage of Cereal Grains and Their Products, Chapter 1: Moisture–Its Significance, Beahavior, and Measurement, W. Harward
 

Hung and S.W. Pixton.
 3 Journal of AOAC, Volume 64, Number 6, 1981, Frank E. Jones and Carroll S. Brickenkamp.
 

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AO_1 

Single-Stage Air-Oven Reference Method for Moisture in Grains, Oilseeds, and Commodities: is the 

difference in weight after drying a ground sample of grain for one hour at 130 oC ± 1 oC (drying time 

is two hours for soybean meal). The following grains and commodities are tested using this method: 

Grains and Oilseeds Commodities 

Description 

Moisture 

Restriction Description 

Sorghum ≤ 16 % Egg Noodles 

Soybeans ≤ 10 % Hominy Grits 

Sunflower ground 50/50 with celite 

Non (for 

moisture 

correction 

of crude oil 

results 

Icing Mix Powder 

Triticale ≤ 16 % Lasagna 

Wheat ≤ 16 % Macaroni 

Macaroni and Cheese 

Rotini 

Rolled Wheat 

Sorghum Grits 

Soybean Meal 

Spaghetti 

Wheat Flour 

Wheat Soy Blend 

Wheat Soy Milk 

Wheat – submitted 

Cited References: AOCS Method Ba 2a-38; AACC Method 44-15A; AOAC Method 925.10; 

ASTM; NIST; Kenyon, A.S., Black, J.C., & Layloff, T.P. (1995); J. Assoc. Off. Anal. Chem. 78, 

1109-1111 

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AO_2 

Two-Stage Air-Oven Reference Method for Moisture in Grains and Oilseeds is the difference 

in weight after air-drying a unground sample of grain until its moisture content is 

≤ 16 % (≤ 10 % for soybeans and ≤ 13 % for rough rice), then drying the ground, air-dried 

sample for one hour at 130 oC ± 1 oC (two hours for soybean meal). The following grains are 

tested using this method: 

Grains and Oilseeds 

Description Moisture 

Restriction 

Barley ˃ 16 % 

Lentils ˃ 16 % 

Oats ˃ 16 % 

Peas ˃ 16 % 

Rice, brown ˃ 16 % 

Rice, milled ˃ 16 % 

Rice, Rough ˃ 13 % 

Rye ˃ 16 % 

Sorghum ˃ 16 % 

Soybeans ˃ 10 % 

Triticale ˃ 16 % 

wheat ˃ 16 % 

Cited References: AACC Method 44-15A;, ASTM; NIST; Kenyon, A.S., Black, J.C., & Layloff, T.P. 

(1995); J. Assoc. Off. Anal. Chem. 78, 1109-1111. 

AO_3 

Air-Oven Reference Method for Moisture in Corn and Beans is the difference in 

weight after drying an unground sample of grain for 72 hours at 103 oC ±1 oC. The 

following grains are tested using this method: 

Grains 

Description Moisture 

Corn Any 

Beans Any 

Cited References: AACC Method 44-15A; ASTM; NIST; Kenyon, A.S., Black, 

J.C., & Layloff, T.P. (1995); J. Assoc. Off. Anal. Chem. 78, 1109-1111. 

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AO_4 

Air-Oven Reference Method for Moisture in Mustard, Canola and Rapeseed is the 

difference in weight after drying an unground sample of grain for one hour at 103 oC 

±1 oC (two hours for soybean meal), repeat the drying and if the difference between 

the 1st and 2nd weight after each drying is greater than 0.01 g the sample is dried for 

an additional hour. The following grains are tested using this method: 

Grains 

Description Moisture 

Mustard Any 

Canola Any 

Rapeseed Any 

Cited References: ISO 665; ASTM; NIST; Kenyon, A.S., Black, J.C., & Layloff, 

T.P. (1995); J. Assoc. Off. Anal. Chem. 78, 1109-1111. 

AO_5 

Air-Oven Reference Method for Moisture in Flaxseed is the difference in weight after 

drying an unground sample of seed for four hours at 103 oC ±1 oC. The following 

grains are tested using this method: 

Grain 

Description Moisture 

Flaxseed Any 

Cited References: AACC Method 44-15A; ASAE Method S352.2; ASTM; NIST; 

Kenyon, A.S., Black, J.C., & Layloff, T.P. (1995); J. Assoc. Off. Anal. Chem. 78, 

1109-1111. 

AO_6 

Air-Oven Reference Method for Moisture in Safflower seeds is the difference in 

weight after drying an unground sample of seed for one hour at 130 oC ±1 oC. The 

following grain is tested using this method: 

Grain 

Description Moisture 

Safflower seeds Any 

Cited References: ASAE Method S352.2; ASTM; NIST; Kenyon, A.S., Black, 

J.C., & Layloff, T.P. (1995); J. Assoc. Off. Anal. Chem. 78, 1109-1111. 

AO_7 

Air-Oven Reference Method for Moisture in Sunflower seeds is the difference in weight 

after drying an unground sample of seed for three hours at 130 oC ±1 oC. The following 

grain is tested using this method: 

Grain 

Description Moisture 

Sunflower seeds Any 

Cited References: AOAC Method Ac 2-41; AOAC Method Ai 2-75; ASTM; NIST; 

Kenyon, A.S., Black, J.C., & Layloff, T.P. (1995); J. Assoc. Off. Anal. Chem. 78, 1109­

1111. 

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Appendix B. Grain Moisture Air-Oven Reference Methods in the United States 

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AO_8 

Air-Oven Reference Method for Moisture in Corn Gluten Feed is the difference in weight 

after drying the ground sample for four hours at 103 oC ±1 oC. The following sample is 

tested using this method: 

Grain 

Description Moisture 

Corn Gluten Feed Any 

Cited References: Method of the Corn Refiners Association; ASTM; NIST; Kenyon, 

A.S., Black, J.C., & Layloff, T.P. (1995); J. Assoc. Off. Anal. Chem. 78, 1109-1111. 

AO_10 through AO_15 are reference methods for other commodities and processes for 

laboratory check samples and equipment maintenance: 

AO_10 100 o C Vacuum Oven Reference Method for moisture in Commodity Samples 

AO_11 Processing the Air-Oven Laboratory Wheat Check Sample 

AO_12 Processing the Air-Oven Laboratory Corn Check Sample 

AO_13 Air-Oven Uniformity Check 

AO_14 Calibrating the Thermometers Used in the Air-Oven Laboratory 

AO_15 Moisture Dish Maintenance and Tare Weight Check Schedule 

Many studies of air-oven reference methods have been conducted over the years since the first use of these reference 

methods. These studies resulted in changes to the air-oven reference methods that improved the accuracy of grain 

moisture meter measurements. The air-oven reference methods are well established in the United States. Stakeholders 

use these reference methods to develop the calibrations for all commercial grain moisture meters and to test these 

devices to provide uniformity in the market place. 

NIST, OWM greatly appreciates the review and comments of Dr. Richard Pierce, USDA, GIPSA during the 

development of this article. 

For additional information concerning this article, please contact Diane Lee by e-mail at diane.lee@nist.gov or the 

Office of Weights and Measures at (301) 975-4004, e-mail at owm@nist.gov. 

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Appendix C. Reference Test Weight Value of per Bushel Value of Grains 

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Appendix C. 

Determining Reference Test Weight per Bushel Value of Grains1 

By G. Diane Lee 

“Test weight per bushel” is a measurement of the weight of a volume of grain required to fill level a Winchester bushel 

measure of 2 150.42 cubic inches (equivalent to 32 quarts) in capacity2

. Test weight per bushel is one of the 

measurements used by the U.S. Department of Agriculture (USDA), Grain Inspection Packers and Stockyards 

Administration (GIPSA) in grain grading. For example, USDA No. 1 hard red spring wheat has a minimum limit for 

test weight per bushel of 58.0 pounds per bushel. In the market place, test weight per bushel is a commercial 

measurement because it affects the market value of grain. When a farmer sells grain, the grain price may be 

“discounted.” If “discounted” for test weight, the farmer receives less money for the grain if the test weight per bushel 

measurement is under a certain specified target weight per bushel, such as 58.0 pounds per bushel. Many grain 

moisture meters, currently in commercial use, that are covered by a National Type Evaluation Program (NTEP) 

Certificate of Conformance, provide grain test weight per bushel measurements that are used to assess the amount of 

money a farmer will receive for grain. As such, the “test weight per bushel” measurement must be verified for 

accuracy. The process used to verify the accuracy of a meter’s test weight per bushel measurement begins in the 

laboratory. Both the NTEP laboratory and state weights and measures laboratories use a reference test weight per 

bushel measurement procedure, and specific equipment to determine the reference test weight per bushel values of 

various grains. Once a reference test weight per bushel value is determined for the grains, the grains are used to verify 

the accuracy of the test weight per bushel feature on meters. Both the NTEP laboratory and State Weights and 

Measures field inspectors verify the accuracy of the weight per bushel measurement of meters by comparing the results 

of the weight per bushel measurement on the meter to the reference “test weight per bushel” value of the grain samples 

that are placed in the meter for measurement. This article addresses the laboratory equipment, equipment maintenance, 

and reference procedures for test weight per bushel because of its importance in determining the accuracy of the test 

weight per bushel measurement of meters. 

Equipment 

To determine reference test weight per bushel 

measurements of grain, use test weight per 

bushel equipment approved by USDA, GIPSA. 

The USDA, GIPSA Equipment Handbook 

includes two lists of GIPSA approved 

equipment: active and inactive. The active 

equipment list includes GIPSA approved 

equipment that is commercially available. The 

inactive equipment list contains GIPSA 

approved equipment no longer manufactured 

or widely marketed, but is still approved for 

use. The equipment used to determine 

reference test weight per bushel values for 

grain are: 

• a quart kettle, 

1 Source: Weights and Measures Connection, Volume 4, Issue 6, September 26, 2013 

2 Circular No. 921 U.S. Department of Agriculture, June 1953 

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Appendix C. Reference Test Weight Value of per Bushel Value of Grains 

•	 a scale specifically designed to measure test weight per bushel, 

•	 a filling hopper, 

•	 an over flow pan, and 

•	 a stroker. 

Figure 1. Test Weight per Bushel Equipment – Active Approved Equipment includes test weight per bushel equipment 

from GIPSA’s active approved equipment list and currently in use at the USDA, GIPSA in Kansas City, Missouri. 

Equipment Maintenance 

The test weight per bushel equipment must be checked and adjusted prior to initial use; and periodically, thereafter, 

as needed. A maintenance schedule of the checks and adjustments made to the equipment must be documented. The 

specifications and maintenance for test weight per bushel equipment are included in GIPSA’s Equipment Handbook, 

which can be downloaded from the USDA, GIPSA Website at: 

http://www.gipsa.usda.gov/fgis/handbook/equip_inspec.aspx 

Procedure for Determining the Reference Test Weight per Bushel Value of 

Grains 

In general, the procedure used to determine the reference test weight per bushel of grain 

is to weigh one dry quart of the grain on a suitable scale that is designed to multiply the 

weight by 32, since there are exactly 32 quarts to a dry bushel. These specially designed 

scales provide a direct reading of test weight per bushel. Since these scales indicate 32 

times the weight of the content in the dry quart, it is very important to follow procedures 

for determining the reference test weight per bushel values of grain. 

The following is a step-by-step procedure to determine the reference test weight per bushel 

values of grain samples that are used to test meters or other equipment used to provide test 

weight per bushel measurements to customers in the marketplace. 

1. Before starting the procedure, ensure that the equipment is positioned 

correctly by placing a level on top of the quart kettle to ensure that it is in a level condition on the 

test stand and position the filling hopper two inches above the top of the quart kettle. Procedures 

for measuring this distance are included in Chapter 5 of the USDA GIPSA Equipment Handbook. 

2. Place the empty quart kettle on the scale; then zero the scale (Figure 2. Zerio Weight of the Empty 

Quart Kettle). 

3. Close the bottom of the fill hopper; place about 11/8 quart of grain in the filling hopper, and place 

the quart kettle on the test stand. 

4. Position the fill hopper over the quart kettle by swiveling the fill hopper 

and fill the kettle from the hopper (Figure 3. Filling the Quart Kettle from 

the Filling Hopper). Do not move the kettle while it is being filled. 

5. Once the quart kettle is full, move the fill hopper away from the quart kettle 

being careful not to move the kettle. 

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Appendix C. Reference Test Weight Value of per Bushel Value of Grains 

6. Hold the stroker on each end with your fingers so that the sides are in a 

vertical position and place it lightly on the edge of the kettle without moving 

the kettle (Figure 3a. Remove Excess Grain). 

7. Stroke the excess grain from the top of the quart kettle in a zigzag motion with 

three full strokes. Each stroke should cover 1

/3 of the top of the kettle (Figure 3b. 

Stroke Pattern: Start with the Stroker at the Edige of the Quart Kettle and Follow a 

ZigZag Pattern). 

Important Note: Scales used to measure test weight 

per bushel are specially designed to provide an 

indication that is 32 times the weight of the grain in 

the quart kettle. So, if the quart kettle contains 1 pound, then the scale will show a 

weight per bushel indication of 32 pounds per bushel (1 to 32 ratio). It is extremely 

important to follow the procedure for step 6, stroking excess grain from the quart kettle 

because too much or too little grain removed, will impact the measurement by a 

multiple of 32 (e.g., if 1 ounce of grain is removed that should have been part of the 

measurement there will be a 2.0 pounds per bushel error in the test weight per bushel 

measurement). 

Example of calculation: 

1 lb = 16 oz
 

1 oz/16 oz = 0.0625 lb,
 

so, 0.0625 lb × 32 = 2.0 lb
 

8. Carefully remove the quart kettle from the stand and weigh the kettle and grain on the 

scale and record your results. (See Figure 4. Weighing the Quart Kettle and Grain) 

In accordance with the National Institute of Standards and Technology (NIST) 

Handbook 44, Specifications, Tolerances, and Other Technical Requirements for Weighing 

and Measuring Devices, Section 5.56.(a) Grain Moisture Meters, paragraph N.1.1. Air-Oven Reference Method 

Transfer Standards, repeat steps 1 through 8, 10 times and average the results for each grain type. The test weight per 

bushel value assigned to the grain samples is the average of 10 measurements. When assigning this value, it must be 

noted that when a standard is used without correction, the combined error and uncertainty in your measurement must 

be less than one-third of the applicable tolerances, in accordance with NIST Handbook 44, Appendix A. Fundamental 

Considerations, Section 3.2. “Tolerances for Standards.” 

The consistent use of proper techniques and proper equipment is key to successfully determining the reference values 

for test weight per bushel. 

Using the prescribed test procedures and correct equipment, as provided in this article along with maintaining your 

equipment in accordance with the USDA, GIPSA Equipment Handbook will reduce the variability and error in your 

reference test weight per bushel measurements made in the laboratory. Practice removing the excess grain from the 

quart kettle will result in better measurement repeatability. Additionally, grain samples with accurate weight per 

bushel values will help to ensure proper testing of meter weight per bushel measurements. 

Resources for Test Weight per Bushel Reference Measurements 

•	 USDA, GIPSA Equipment Handbook at:
 

http://www.gipsa.usda.gov/Publications/fgis/handbooks/equip_insphb.html.
 

•	 Circular No. 921 “The Test Weight per Bushel of Grain: Methods of Use and Calibration of the Apparatus,” 

June 1953, United States Department of Agriculture. 

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Appendix C. Reference Test Weight Value of per Bushel Value of Grains 

______________________________________________________________________________________________________ 

This publication is available free of charge from: http://dx.doi.org/10.6028/NIST.HB.159

For additional information concerning this article you may contact Diane Lee of the NIST, Office of Weights and 

Measures (OWM) by e-mail at diane.lee@nist.gov, or contact the office at owm@nist.gov, phone (301) 975-3998. 

Note: It is policy of the National Institute of Standards and Technology to use metric units of measurement 

in all of its publications. However, in this newsletter the references to inch-pound units are used as they 

are commonly used in industry practice and in source documentation. 

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