Figure 2. Weight set and case
j. The usual 1-2-2-5 weight arrangement and the recently established 1-2-3-6 sequences
are related to a binary-coded-decimal (BCD) sequence. In some instances a true binary
sequence has replaced the BCD sequence because the use of four weights in 16 possible
combinations expands their range by a factor of 1.6 without additional decoding
problems. The consideration of BCD versus binary coded systems is a matter of
decreasing the search-steps (trail and error weight matching) to a minimum, and at the
same time reducing the maximum number of weights required.
k. Materials
(1) Weight measurements are subjected to errors caused by humidity, absorption,
desorption, wear, influence of electrostatic charges, and temperature effects.
These effects tend to cause temporary or permanent changes in the value of the
standard weights, thereby producing weight measurement errors. In an effort to
reduce the errors caused by the changes in materials, large mass standards are
usually restricted to the following material:
Platinum-iridium (90%--10%)
Platinum
Stainless steel (25% chromium, 20% nickel)
Nonmagnetic nickel chromium (80% - 20%)
Brass - plated with rhodium, platinum, or chromium
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