Cryogenic Fluids Density Reference System: Provisional Accuracy Statement (1980) Page: 37

                                
The required densities are:

ps = 2.33078 g/cm3 (silicon at 110 K)
pw = 8.4     g/cm3 (Brass at ambient temperature)
and pg is determined as described in Appendix 9.3.
The weighing was done with an 0.1 mg sensitivity beam balance using a set
of class S weights. The various weights were transposition-weig:ed, and buoyancy
was corrected. These weights should be periodically checked to assure the
values do not change with use due to chipping, scratching, oxidation, dirt, etc.
Even though the silicon crystal is large and thus provides more sensitivity,
this electronic balance is less sensitive than that in the DRS and the weighing
method is inferior so the measurement uncertainty is greater. The electronic
balance in the IR densimeter is capable of measuring weights of 0 to 400 g, but
its resolution is only   10 mg when equipped with the factory readout unit. A
resolution of about 1 mg was sought using a more sensitive digital volt-meter is
substituted for the factory readout. The method of comparing the crystal weight
in liquid to a reference weight was used, though the accuracy of this method
compared to a direct weighing of the crystal was not examined. The direct
weighing method had a disadvantage in these measurements because a capacitor
placed across the analog output of the balance to reduce the noise level resulted
in a iong system time constant. The accuracy of the density measurements by the
IR densimeter are also affected by the accuracy of the required gas bouyancy
corrections to the reference weight and the small scale calibration weight. The
method of calculating this buoyancy correction is detailed in Appendix 9.3.

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