I have used a RCBS digital scale for the last 30 years. I tare the pan to zero and it reads 140gr. Occasionally I’ve noticed it jumps to 141 when I remove the pan, signaling me to re-zero to 140.
I have 2 sets of weights from my Pharmacy career: apothecary and Metric. I can’t imagine one would have any weights more accurate than those we used to produce pharmaceutical products at a retail level. They were/are manufactured by Henry Troemner, Inc., from Philadelphia, PA., and were a part of my college admission purchase requirement in 1960.
Based on 1.0 Gm = 15.432 grains, this is what I would expect my 20- and 50-gram weights supplied with the RCBS scale to produce:
20 Gm = 308.64 grains. My scale says 308.1 and 19.98 Gm.
50Gm = 771.6 grains. My scale says 770.8 grains and 49.95 Gm
With the Apothecary weights, it becomes more accurate:
Set for “grains” I get the following results:
5 grains weight = 5.0 grains
2 grains = 2.0
1 grain = 1.0
0.5 grain = 0.5
One Scruple ( apothecary) = 20 grains. My scale delivers 19.9 grains.
If I set the tared schedule to “Grams” and 0.000., I get
500mg = 0.5 Gm
200mg = 0.20Gm
100mg = 0.9 Gm
50mg = 0.04 Gm that instantly converts to 0.00
20mg = 0.02Gm that again, instantly flips to 0.00
10mg =0.00 = no reading
So it would appear that my RCBS scale is more accurate in the grain mode, and that explains to discrepancy with the weights supplied in grams. However, in practice, as I said above, I find that the tared (zero) weight of 140 occasionally jumps to 141. This means my tared pan weight has increased by 1.0 grain, so if my target weight is 50 gr, that particular load only has 49 gr. I have never experienced the opposite situation, i..e, an increase in the charge due to a decrease in the tared pan weight.
So any time I remove the pan to dump the charge, I observe the tared weight of 140. Then I am assured my measured weight is the one desired. If the tared pan jumps to 141, I reset it to zero again, and re-weigh that charge.
I will say, this change is not common; I do not have any significant drafts in my area of reloading and I do have a surge protector plugged into the receptacle, followed by my plug for the weight scale.