Forgive my intrusion on the US side (I collect ancients) but I need help only a US collector might know. My coin scales stopped working so I bought a new (cheap) one supposedly weighing coins to 100g to two decimal places (.01g). Now I realize that a cheap scales might not be accurate to that last digit but I'm trying to calibrate the scales as best I can. My old scales came with a reference weight of 50g but the new one requires 100g for the calibration process. I thought that I could make up the difference using US coins - particularly nickels which the mint site gives as 5.000g http://www.usmint.gov/about_the_mint/?action=coin_specifications IMHO, three digits is absurd to maintain with any degree of consistency but just how much variation is expected from a sampling of nickels? My pocket change contained four nickels which ranged from 5.09g (1959P worn to F) to 4.92g (2010P looks AU). Weighing the coins several times suggests the scales is consistent to the individual coin. Is this an accurate result for production run coins or would I possibly be able to get a roll of brand new nickels and expect better consistency? Is it common to find individual nickels over 5.0g?
I would take a roll of jeffersons with the 50 gram reference wt. to a person who has a more precise calibrated scale and put the 50 gr weight and weigh it to be sure first, and then add new Jeffersons until it reached 100.00 gr. You can mix coins until you get a reasonable reference weight. Jewelers, pharmacists, High school/college science instructors, etc. The tolerances allowed coins do not individually allow them to be references. If it is a school, with multiple scales they may have a spare reference weight you could borrow and do it at home more leisurely.
The problem with trying to use coins as a calibration weight is that their weight does vary. Modern mint tolerances are not as tight as they used to be. As a rule of thumb about a 1% tolerance used to be the standard. But I would think even that would be enough to screw up a calibration when you are talking 50 grams. Following Jim's advice would probably be a pretty good idea. Of course you could just buy another 50 gram weight.
I found a brass 50g weight that came with an old balance scale. It had drill marks on the bottom where it had been adjusted at the factory so I thought it might be more accurate. It weighs almost .5g less than the other one I have. Again considering the scale consistently gives the same results for the same coin, I think my next step will be to fool it in calibration so it matches the weight of coins I bought from a dealer I know has a better scale. An accurate weight for calibration will cost more than the scale being calibrated.
