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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