c. Since all mass standards (weights) are basically the same, with exceptions such as
manufacturing tolerances and requirements, we restrict our instruction to weight
classification 1, which is typical of all classifications. Classification 1 is made up of four
separate groups or classes of weights, which are:
Class J- Metric weights designed as mg standards.
Class M- Metric weights designed as reference standards for work of the highest
precision.
Class S -Metric weights designed as working standards for the calibration of other
weights.
Class S-1-Precision weights used for routine analytical work. Included weights
are expressed in units of avoirdupois, apothecary, and troy, as well as metric
weights.
d. Although the information presented is used on tolerances, denominations, and
materials, weights in all classes must meet the following NBS requirements:
Material - hardness, corrosion resistance, contamination, magnetic properties,
density.
Design - general shape, thickness, number of pieces.
Surface - irregularities, porosity.
Denominations - system of units, numerical series.
Tolerances - acceptance, maintenance.
Marking - identification.
Handling - lifters.
e. Tolerances. We don't include all of the classes into which weights are divided. The
classes identified are included so that you realize differences between weights used in
your laboratory. The list which follows compares acceptance and maintenance tolerances
for some of the different classes of weights.
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