Table 1.

One-sigma uncertainties (in parts per million) from various sources in the redetermination of R

I (Volume)2/3
density of mercury at 20 °C	0.28
storage and handling of mercury	0.20
thermal expansion of mercury (0–20 °C)	0.67
random error of volume measurements	0.20
corrections from weighing configuration to acoustics configuration	0.10
mass of counterweights	0.14
II Temperature
random error of calibrations	0.8
temperature gradient	0.4
III M/γ0
Ar-40 standard	0.7
comparison of working gas to Ar-40	0.4
IV Zero-pressure limit of (f0n/v0n)2
s.d. of $c_0^2$ from 70 observations at 14 pressures	0.68
thermal boundary layer correction (0.3% of thermal conductivity)	0.30
possible error in location of transducers	0.55
Square root of the sum of the squares	1.7