Relationship between the mass and conventional mass of a weight in Calibration

The conventional mass value of a body is equal to the mass mc of a standard that balances this body under conventionally chosen conditions. The unit of the quantity "conventional mass" is the kilogram 

The conventionally chosen conditions are: 
tref = 20 C 0 = 1.2 kg m-3 c = 8 000 kg m-3 

The conventional mass has the same unit as mass, because its values are defined through the multiplication of a mass by a dimensionless quantity. 

If the mass of a weight is known (e.g. from a calibration certificate) its conventional mass can be calculated according to this definition from the following formula:
This definition shows that the conventional mass of a weight made of stainless steel which has a density close to = 8000 kg m-3 deviates from its mass by only a small amount.
For other materials, the relative deviation of mc from m ranges from about – 3 10-4 for aluminium to + 10-4 for platinum. Nevertheless, the difference between the conventional mass value of a weight and its physical mass can be significant even for weights made of stainless steel.

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