[nulld3v]

Most of the budget scales I've seen are accurate to <0.1g. If in doubt, grab a cheap set of calibration weights for $20, I have 2 sets from China and both are accurate to <0.01g on all the weights from 1g up to 200g.

Obviously if you have the money, you can buy actual certified ASTM weights, but they are insanely expensive.

[shrx]

You can calibrate the scale with coins as well. They have a pretty well defined mass.

[esperent]

Many countries don't have coins unfortunately, including the one where I live. Also, is that true for all coins in every country?