Since 1959, land surveyors and other geospatial professionals have had two primary standards to measure the length of a foot – the United States survey foot and the international foot. Both have been supported by the NOAA’s National Geodetic Survey and the National Institute of Standards and Technology. The difference between these two measurements is small and barely noticeable in modern-day use and is a function of their relationship to the standardized meter. A United States survey foot is expressed as a fraction – about 1200/3937 meters – while an international foot is expressed as a decimal. The difference is only about one-hundredth of a foot per mile. When you measure or use coordinates spanning hundreds and thousands of miles, that slight difference could reach a few to several feet. This is why the NIST and NOAA are retired to the U.S. survey foot and standardizing the international foot. To learn more about that Class F replacement, read on!
The Status of Class F Weights
There were plenty of significant changes used in the NIST HB 105-1 documentary standard, but the most challenging transition for users of the HB 105-1 seems to be the requirement that no new NIST Class F weights will be placed into service for usage in testing commercial weighing equipment after January of 2020. Any existing NIST Class F field standard weights might continue to be used, provided they demonstrate mass stability and are maintained correctly. However, their suitability will still be limited to use as field standard weights for verification in the NIST Handbook 44 weighing systems designated in Accuracy Classes III, IIIL, and IIII.
Legal Requirements for Any Field Standard Weights
Retiring HB 105-1 was discussed initially. However, to help minimize the impact on the various states and weights and measures jurisdictions with the specific handbook cited in their legal documents, the revised NIST HB 105-1 has been maintained as a NIST Handbook. Regardless of the accuracy classification, field standard weights must still comply with the NIST HB 105-1 requirement. However, that document now directs the users to one of the standards for the specifications and tolerances of new weights to be used for weighing device field tests:
– ASTM E617, standard specification of any lab weights and precision mass standards
– OIML R111-1, this is the recommendation, for any international measurements, for different weight classes
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