November 2006 

Grain Moisture Meter (GMM) Series 

Part 1 – Overview of GMM Series Topics 

By G. Diane Lee 

The NIST Weights and Measures Division is nearing completion of a new field manual 

for the evaluation of commercial grain moisture meters (GMMs). As a preview to this 

manual and to provide weights and measures officials with information to increase 

awareness of GMMs, a series of articles will be provided in the Weights and Measures 

Quarterly to give an overview of the economic impact of GMMs and provide a preview 

to the field manual by discussing the various aspects of measuring moisture in grain. 

This article (Part 1) outlines the subjects included in the series and provides highlights of 

each part. 

Part 2 - Economic Impact. Although few in numbers compared to other commercial 

devices, GMMs have a high dollar impact per device. Part 2 will explore the amount of 

grain measured, the value of grain measured by GMMs in the United States, and the 

potential monetary loss due to inaccuracies in these meters. 

Part 3 - Grain Moisture Meter Measurement Technology. Currently, two technologies—

dielectric and near infrared—are used in commercial devices in the United States to 

measure grain moisture. GMMs measure an optical or electrical property of the grain. 

When these optical or electrical properties are compared to known grain moisture values, 

a calibration for the grain can be developed. Based on this calibration, the device can 

provide a moisture reading related to the measurement of the optical or electrical property 

of that grain. The September 2006 Weights and Measures Quarterly article, “What do 

Grain Moisture Meters Measure and How are They Calibrated?” addressed the dielectric 

technology. Part 3 of this series will review near infrared technology. 

Part 4 - Field Test Methods, Testing Apparatus and Equipment. The most widely used 

test method for the evaluation of GMMs in the United States uses grain as the transfer 

standard. Unlike other commercial devices, the standards used to test moisture meters are 

biological samples that require preparation and care to maintain. There are various types 

of equipment and apparatus needed to test GMMs, including storage and transport 

containers, temperature measuring devices, and refrigeration. Part 4 of this series will 

review the maintenance of grain transfer standards and the apparatus and equipment 

needed to test these devices. 

Part 5 - Field Inspection and Test. Commercial GMMs, as with other commercial 

devices are inspected and tested in accordance with NIST Handbook 44. Specific test 

procedures are now included in the new field manual. The February 2004 Weights and 

Measures Quarterly article “Testing Grain Moisture Meters” provided some guidance in 

testing GMMs. Part 5 of this series will elaborate on the Evaluation Procedure Outline 

and test procedures included in the new GMM field manual. 

 
Part 6 - Laboratory Grain Sample Preparation. Grain transfer standards are developed in 

a laboratory. The laboratory must follow appropriate grain handling, collection and 

cleaning procedures along with having the appropriate equipment and laboratory 

environment to ensure grain transfer standards are adequate and available for GMM 

testing. Part 6 of this series will review Appendix C of the new field manual that 

includes laboratory procedures, equipment, and facilities needed to develop grain transfer 

standards. 

 

Hopefully, this series of articles will increase State awareness of GMMs, facilitate the use 

of the new GMM field manual, and provide those States which have a high grain 

production and possible high monetary loss due to inaccuracies in GMMs with the tools 

needed to develop a GMM testing program in their State. 

If you have any questions, comments, or suggestions on other grain moisture topics that 

you would like to see covered in the upcoming series, please contact G. Diane Lee by email at diane.lee@nist.gov.