Inside SOP 14: gravimetric volume calibration — mass in, litres out

The most accurate way to measure a volume is to weigh it. SOP 14 in the library is the gravimetric method for volume standards: fill with distilled water, weigh, and convert mass to volume through water's density at the measured temperature — with air buoyancy corrected, since a kilogram of water displaces a litre of air's worth of buoyancy.

The conversions carry the physics: water density as a function of temperature (and its isotopic and purity caveats), the cubical expansion of the vessel material referred back to its reference temperature, and the buoyancy term. Each correction gets a line in the uncertainty budget, and temperature measurement usually dominates.

SOP 13 applies the same method to laboratory glassware, where GMP 3's meniscus-reading practice — sight line, lighting, the bottom of the curve — decides whether the last digit means anything. The trio makes a complete small course in volume metrology, free and page-searchable.