G-UR. 1.1. suitability of equipment, NIST handbook 44
A primary concern in determining the appropriateness of a scale for this application is the value of the scale division. The minimum load (mass on scale) to be weighed should be equal to at least 50 scale divisions. The reason for this is to minimize the error in the weighing process caused by the uncertainty of one-half the value of a scale division.
Examples:
If the smallest load is 5 grams, the value of scale division should be no larger than 0.1 gram.
If the smallest load is 0.1 oz troy, the value of scale division should be no larger than 0.002 oz troy or 0.04 dwt.
If the smallest load is 0.5 oz troy, the value of scale division should be no larger than 0.01 oz troy or 0.2 dwt.
Posting value comparisons
To avoid misunderstandings with customer's, the appropriate common denominator in the scale of precious metals is troy weight, when determining which is the best sales value when some buyers use equipment graduated in troy units and others use equipment in other than troy units. Anyone using a scale graduated in other than troy weight should express the buying price in both troy and the other unit.
Example:
$100 / troy ounce
$3.215 / gram
$5 / pennyweight (dwt)
$3.215 / gram
$10 / pennyweight (dwt)
$6.43 / gram
In addition, the appropriate unit equivalents and conversion factors should be posted.
