pooled relative standard deviation

https://doi.org/10.1351/goldbook.P04757
See: pooled standard deviation, relative standard deviation
Source:
PAC, 1981, 53, 1805. 'Assignment and Presentation of Uncertainties of the Numerical Results of Thermodynamic Measurements' on page 1821 (https://doi.org/10.1351/pac198153091805)