Often used to calibrate precision scales, these highly accurate test weights come with a certificate of calibration traceable to NIST that states they’ve passed a test for accuracy. They are marked with their weight.

Class 1 weights are highly accurate and used as a reference standard for calibrating other calibration weights. They are also good for calibration of microbalances and analytical balances.

Class 4 weights are good for calibrating precision balances, laboratory balances, and digital scales.