Approximately 900 validated weights (mass stacks not included) are currently available in Working Group 1.12, with values ranging between 1 mg and 20 kg. The accuracy classes are E1 (reference standards only), E2, F1, F2, M1 and M3. The material for F1 and better is stainless steel, for F2 and worse brass is also used, and some of the 10 kg and 20 kg weights are of cast iron. The working standards are calibrated by 1.12, the reference standards by the PTB working group 1.11.