Certified Scales

To weigh metals in trade and gunpowder for repackaging and resale, a certified scale is necessary.  That is, one with a pedigree traceable back to standardized weights, which is legal for business use.  Required accuracy and maximum load determine what kind of scale is needed.  For 1-gram accuracy, the CAS ED series looks good.  For 0.1-gram/0.005-ozt accuracy, there's the Citizen CZ1200.