Handbook 44 – 2012 5.56.(a) Grain Moisture Meters

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Table of Contents

Section 5.56.(a) Grain Moisture Meters ............................................................................ 5-41

A. Application .................................................................................................................................................. 5-41

A.1. General Code. .....................................................................................................................................5-41

A.2. Exceptions...........................................................................................................................................5-41

A.3. Type Evaluation..................................................................................................................................5-41

A.4. Additional Code Requirements...........................................................................................................5-41

S. Specifications............................................................................................................................................... 5-41

S.1. Design of Indicating, Recording, and Measuring Elements................................................................5-41

S.1.1. Digital Indications and Recording Elements.......................................................................5-41

S.1.2. Selecting or Recording Grain or Seed Type and Class. ......................................................5-42

S.1.3. Operating Range..................................................................................................................5-43

S.1.4. Value of Smallest Unit. .......................................................................................................5-43

S.1.5. Operating Temperature. ......................................................................................................5-43

S.2. Design of Grain Moisture Meters. ......................................................................................................5-43

S.2.1. Minimum Sample Size........................................................................................................5-43

S.2.2. Electric Power Supply.........................................................................................................5-44

S.2.3. Level Indicating Means.......................................................................................................5-44

S.2.4. Calibration Integrity. ...........................................................................................................5-44

S.2.5. Provision for Sealing...........................................................................................................5-44

S.2.6. Determination of Quantity and Temperature. .....................................................................5-46

S.3. Accessory Equipment. ........................................................................................................................5-46

S.4. Operating Instructions and Use Limitations. ......................................................................................5-46

N. Notes............................................................................................................................................................. 5-46

N.1. Testing Procedures..............................................................................................................................5-46

N.1.1. Air Oven Reference Method Transfer Standards. ...............................................................5-46

N.1.2. Minimum Test.....................................................................................................................5-47

N.1.3. Meter to Like-Type Meter Method Transfer Standards. .....................................................5-47

T. Tolerances.................................................................................................................................................... 5-47

T.1. To Underregistration and to Overregistration. ....................................................................................5-47

T.2. Tolerances...........................................................................................................................................5-47

T.2.1. Air Oven Reference Method. ..............................................................................................5-47

T.2.2. Meter to Like-Type Meter Method. ....................................................................................5-47

T.3. For Test Weight Per Bushel Indications or Recorded Representations. .............................................5-48

UR. User Requirements ..................................................................................................................................... 5-48

UR.1. Selection Requirements. .....................................................................................................................5-48

UR.1.1. Value of the Smallest Unit on Primary Indicating and Recording Elements. .....................5-48

UR.1.2. See G-UR.1.2. Environment. .............................................................................................5-48

UR.2. Installation Requirements. ..................................................................................................................5-48

UR.3. Use Requirements. ..............................................................................................................................5-48

UR.3.1. Operating Instructions.........................................................................................................5-48

UR.3.2. Other Devices Not Used for Commercial Measurement.....................................................5-48

UR.3.3. Maintaining Integrity of Grain Samples..............................................................................5-49

UR.3.4. Printed Tickets. ...................................................................................................................5-49

UR.3.5. Accessory Devices. .............................................................................................................5-49

UR.3.6. Sampling. ............................................................................................................................5-49

UR.3.7. Location. .............................................................................................................................5-49

UR.3.8. Level Condition...................................................................................................................5-49
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UR.3.9. Current Calibration Data. ....................................................................................................5-49

UR.3.10. Posting of Meter Operating Range......................................................................................5-49
Handbook 44 – 2012 5.56.(a) Grain Moisture Meters

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Section 5.56.(a) Grain Moisture Meters

Section 5.56. was reorganized into two sections beginning with the 1997 Edition of NIST Handbook 44. This 

Section, 5.56.(a), applies to all NTEP grain moisture meters. It also applies to any grain moisture meter 

manufactured or placed into service after January 1, 1998. 

(Code reorganized and renumbered 1996)

A. Application

A.1. General Code. – This code applies to grain moisture meters, that is, devices used to indicate directly the 

moisture content of cereal grain and oil seeds. The code consists of general requirements applicable to all moisture 

meters and specific requirements applicable only to certain types of moisture meters. Requirements cited for “test 

weight per bushel” indications or recorded representations are applicable only to devices incorporating an automatic 

test weight per bushel measuring feature.

(Amended 2003)

A.2. Exceptions. – This code does not apply to devices used for in-motion measurement of grain moisture content 

or seed moisture content.

A.3. Type Evaluation. – The National Type Evaluation Program (NTEP) will accept for type evaluation only 

those devices that comply with this code. State enforcement will be based upon the effective dates identified with 

each requirement when specific dates are shown.

(Added 1993)

A.4. Additional Code Requirements. – In addition to the requirements of this code, 5.56.(a) Grain Moisture 

Meters shall meet the requirements of Section 1.10. General Code.

S. Specifications

S.1. Design of Indicating, Recording, and Measuring Elements.

S.1.1. Digital Indications and Recording Elements.

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

(b) The minimum height for the digits used to display moisture content shall be 10 mm.

(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.

(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.

(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).

(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).
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(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.

(Added 1995)

(Amended 1993, 1994, 1995, 1996, and 2003)

S.1.2. Selecting or Recording Grain or Seed Type and Class. – Provision shall be made for selecting and 

recording the type and class or multi-class 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.

(Amended 1993, 1995, and 2007)

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]

(Table Added 1993) (Amended 1995, 1998, and 2007)
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S.1.3. Operating Range. – A meter shall automatically and clearly indicate when the operating range of the 

meter has been exceeded. The operating range shall specify the following:

(a) 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.

(b) 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.

(c) 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.

(Amended 2003)

(d) 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.

(Added 1993) (Amended 1995)

S.1.4. Value of Smallest Unit. – The display shall permit moisture value determination to both 0.01 % and 

0.1 % resolution. The 0.1 % resolution is for commercial transactions; the 0.01 % 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.

(Amended 2003)

S.1.5. Operating Temperature.

(a) 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.

(b) 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.

(c) If the manufacturer specifies a temperature range, the range shall be at least 20 °C (36 °F).

(Added 1993) (Amended 1995 and 1996)

S.2. Design of Grain Moisture Meters.

S.2.1. Minimum Sample Size. – Meters shall be designed to measure the moisture content of representativesize grain samples. The minimum allowable sample size used in analysis shall be 100 g or 400 kernels or seeds, 

whichever is smaller.

(Added 1993) (Amended 1995)
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S.2.2. Electric Power Supply.

S.2.2.1. Power Supply, Voltage and Frequency.

(a) 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.

(b) Battery-operated instruments shall not indicate or record values outside the applicable tolerance 

limits when battery power output is excessive or deficient.

S.2.2.2. Power Interruption. – A power interruption shall not cause an indicating or recording element 

to display or record any values outside the applicable tolerance limits.

(Added 1988)

S.2.3. Level Indicating Means. – 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 level-indicating means shall be readable without removing any meter parts requiring a tool.

(Added 1988) (Amended 1994)

S.2.4. Calibration Integrity.

S.2.4.1. Calibration Version. – 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.

(Added 1993) (Amended 1995 and 2003)

S.2.4.2. Calibration Corruption. – If calibration constants are digitally stored in an electronically 

alterable form, the meter shall be designed to make automatic checks to detect corruption of calibration 

constants. An error message must be displayed if calibration constants have been electronically altered.

(Added 1993) (Amended 1995)

S.2.4.3. Calibration Transfer. – The instrument hardware/software design and calibration procedures 

shall permit calibration development and the transfer of calibrations between instruments of like models 

without requiring user slope or bias adjustments.

[Note: Only the manufacturer or the manufacturer’s designated service agency may make standardization 

adjustments on moisture meters. This does not preclude the possibility of the operator installing 

manufacturer-specified calibration constants under the instructions of the manufacturer or its designated 

service agency.] Standardization adjustments (not to be confused with grain calibrations) are those 

physical adjustments or software parameters which make meters of like type respond identically to the 

grain(s) being measured.

[Nonretroactive as of January 1, 1999]

(Added 1994) (Amended 1998)

S.2.5. Provision for Sealing. – 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) before any 

change that affects the metrological integrity of the device can be made to any mechanism.
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Table S.2.5. 

Categories of Device and Methods of Sealing

Categories of Device Methods of Sealing

Category 1: No remote configuration capability. Seal by physical seal or two event counters: one for 

calibration parameters (000 to 999) and one for 

configuration parameters (000 to 999). If equipped 

with event counters, the device must be capable of 

displaying, or printing through the device or through 

another on-site device, the contents of the counters.

Category 2: Remote configuration capability, but 

access is controlled by physical hardware.

A device shall clearly indicate that it is in the remote 

configuration mode and shall not be capable of 

operating in the measure mode while enabled for 

remote configuration.

The hardware enabling access for remote 

communication must be at the device and sealed using 

a physical seal or two event counters: one for 

calibration parameters (000 to 999) and one for 

configuration parameters (000 to 999). If equipped 

with event counters, the device must be capable of 

displaying, or printing through the device or through 

another on-site device, the contents of the counters.

Category 3: Remote configuration capability access 

may be unlimited or controlled through a software 

switch (e.g., password).

When accessed remotely for the purpose of modifying 

sealable parameters, the device shall clearly indicate 

that it is in the configuration mode and shall not be 

capable of operating in the measuring mode.

An event logger is required in the device; it must 

include an event counter (000 to 999), the parameter 

ID, the date and time of the change, and the new value 

of the parameter (for calibration changes consisting of 

multiple constants, the calibration version number 

may be used rather than the calibration constants). A 

printed copy of the information must be available 

through the device or through another on-site device. 

The event logger shall have a capacity to retain 

records equal to 25 times the number of sealable 

parameters in the device, but not more than 

1000 records are required. (Note: Does not require 

1000 changes to be stored for each parameter.)

Category 3a: No remote capability, but operator is 

able to make changes that affect the metrological 

integrity of the device (e.g., slope, bias, etc.) in normal 

operation.

Same as Category 3

Category 3b: No remote capability, but access to 

metrological parameters is controlled through a 

software switch (e.g., password).

Same as Category 3

[Nonretroactive as of January 1, 1999]

(Amended 1998)

Note: Zero-setting and test point adjustments are considered to affect metrological characteristics and must be sealed.

(Added 1993) (Amended 1995 and 1997)
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S.2.6. Determination of Quantity and Temperature. – 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. [Nonretroactive as of January 1, 2004]

(Added 1994) (Amended 1995 and 2003)

S.3. Accessory 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.

S.4. Operating Instructions and Use Limitations. – The manufacturer shall furnish operating instructions for 

the device and accessories that include complete information concerning the accuracy, sensitivity, and use of 

accessory equipment necessary in obtaining a moisture content. Operating instructions shall include the following 

information:

(a) name and address or trademark of the manufacturer;

(b) the type or design of the device with which it is intended to be used;

(c) date of issue;

(d) the kinds or classes of grain or seed for which the device is designed to measure moisture content and test 

weight per bushel; and

(Amended 2003)

(e) the limitations of use, including but not confined to the moisture measurement range, grain or seed 

temperature, maximum allowable temperature difference between grain sample and meter, kind or class of 

grain or seed, moisture meter temperature, voltage and frequency ranges, electromagnetic interferences, 

and necessary accessory equipment.

(Added 1984)

N. Notes

N.1. Testing Procedures. – Field evaluation of grain moisture meters shall be performed by one of the following 

methods:

N.1.1. Air Oven Reference Method Transfer Standards. – 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).

(Amended 1992, 2001, and 2003)
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N.1.2. Minimum Test. – A minimum test of a grain moisture meter shall consist of tests using samples (need 

not exceed three) of each grain or seed type for which the device is used, and for each grain or seed type shall 

include the following:

(a) tests of moisture indications, using samples having at least two different moisture content values 

within the operating range of the device; and

(b) if applicable, tests of test weight per volume indications, with at least the lowest moisture samples used 

in (a) above.

(Added 2003)

(Amended 1986, 1989, and 2003)

N.1.3. Meter to Like-Type Meter Method Transfer Standards. – Properly standardized reference meters 

using National Type Evaluation Program approved calibrations shall be used as transfer standards. A reference 

meter shall be of the same type as the meter under test. Tests shall be conducted side-by-side using, as a 

comparison medium, grain samples that are clean and naturally moist, but not tempered (i.e., water not added).

(Added 2001)

T. Tolerances

T.1. To Underregistration and to Overregistration. – The tolerances hereinafter prescribed shall be applied to 

errors of underregistration and errors of overregistration.

T.2. Tolerances.

T.2.1. Air Oven Reference Method. – Maintenance and acceptance tolerances shall be as shown in 

Table T.2.1. Acceptance and Maintenance Tolerances Air Oven Reference Method. Tolerances are expressed 

as a fraction of the percent moisture content of the official grain sample, together with a minimum tolerance.

(Amended 2001)

Table T.2.1. 

Acceptance and Maintenance Tolerances Air Oven Reference Method

Type of Grain, Class, or 

Seed Tolerance Minimum Tolerance

Corn, oats, rice, sorghum, 

sunflower

0.05 of the percent

moisture content

0.8 %

in moisture content

All other cereal grains 

and oil seeds

0.04 of the percent

moisture content

0.7 %

in moisture content

(Amended 2001)

T.2.2. Meter to Like-Type Meter Method. – Maintenance and acceptance tolerances shall be as shown in 

Table T.2.2. Acceptance and Maintenance Tolerances Meter to Like-Type Meter Method. The tolerances shall 

apply to all types of grain and seed.

(Added 2001)
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Table T.2.2. 

Acceptance and Maintenance Tolerances Meter to Like-Type Meter Method

Sample Reference Moisture Tolerance

Up to 22 % 0.5 %

in moisture content

(Added 2001)

T.3. For Test Weight Per Bushel Indications or Recorded Representations. – The maintenance and acceptance 

tolerances on test weight per bushel indications or recorded representations shall be as shown in 

Table T.3. Acceptance and Maintenance Tolerances Test Weight per Bushel. Tolerances are (+) positive or 

(−) negative with respect to the value assigned to the official grain sample.

(Amended 1992 and 2003)

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)

UR. User Requirements

UR.1. Selection Requirements.

UR.1.1. Value of the Smallest Unit on Primary Indicating and Recording Elements. – The resolution of 

the moisture meter display shall be 0.1 % moisture and 0.1 pounds per bushel test weight during commercial 

use.

(Amended 2003)

UR.1.2. See G-UR.1.2. Environment.

UR.2. Installation Requirements. – The grain moisture meter shall be installed in an environment within the 

range of temperature and/or other environmental factors specified in the operating instructions.

UR.3. Use Requirements.

UR.3.1. Operating Instructions. – The operating instructions for the use of the grain moisture meter shall be 

readily available to the user, service technician, and weights and measures official at the place of installation. It 

shall include a list of accessory equipment and the kinds of grain or seed to be measured with the moisture 

meter.

(Amended 1988)

UR.3.2. Other Devices Not Used for Commercial Measurement. – 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.”
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UR.3.3. Maintaining Integrity of Grain Samples. – Whenever there is a time lapse (temperature change) 

between taking the sample and testing the sample, means to prevent condensation of moisture or loss of 

moisture from grain samples shall be used. For example, a cold grain sample may be kept in a closed container 

in order to permit the cold grain to come to the operating temperature range of the meter before the grain 

moisture measurements are made.

UR.3.4. Printed Tickets.

(a) Printed tickets shall be free from any previous indication of moisture content or type of grain or seed 

selected.

(b) 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.

(Amended 1993, 1995, and 2003)

UR.3.5. Accessory Devices. – 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.

UR.3.6. Sampling. – A grain sample shall be obtained by following appropriate sampling methods and 

equipment. These include, but are not limited to grain probes of appropriate length used at random locations in 

the bulk, the use of a pelican sampler, or other techniques and equipment giving equivalent results. The grain 

sample shall be taken such that it is representative of the lot.

UR.3.7. Location. – See G-UR.3.3. Position of Equipment.

UR.3.8. Level Condition. – If equipped with a level indicator, a meter shall be maintained in a level 

condition.

(Added 1988)

UR.3.9. Current Calibration Data. – Grain moisture determinations shall be made using only the most 

recently published calibration data.

(Added 1988)

UR.3.10. Posting of Meter Operating Range. – 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:

(a) The temperature range over which the meter may be used and still comply with the applicable 

requirements. If the temperature range varies for different grains or seed, the range shall be specified 

for each.

(b) The moisture range for each grain or seed for which the meter is to be used.

(c) The temperature range for each grain or seed for which the meter is to be used.

(d) The maximum allowable difference in temperature that may exist between the meter and the sample 

for which an accurate moisture determination can be made.

(Added 1988)
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