Dissemination of South African Mass Standards from the National Prototype

The South African national standard for mass, prototype No.56 of the Kilogram is a cylinder of platinum-iridium alloy maintained by NMISA and is calibrated once in ten years at the BIPM. It is traceable to the international prototype in BIPM and it is currently serving as a national primary standard of mass. The mandate of the NMISA Mass laboratory is to maintain and disseminate the value of the kilogram. To ensure this NMISA utilises two high quality (Class E1) weights as transfer standards calibrated against the prototype using an automated system and a double substitution method of measurements. Other working standards, ranging from 1mg to 20kg, are also utilised. The working standards are calibrated by sub-division and multiplication methods using a single reference standard. This paper presents the multiple and sub-multiple methods used at the NMISA to disseminate the value of the kilogram and provide traceability of customer standards