Because Brix refractometers used for brewing are meant to read pure sucrose values only, a brewer cannot take a direct gravity reading while the beer is fermenting or has finished fermenting. This is because the alcohol present in the fermenting beer skews the refractive index.

However, using ProMash a brewer can indeed take gravities reading during and after fermentation using The Gravity During Fermentation Refractometer Utility. All that is needed is the Original Gravity of the beer and a refractometer reading of the current gravity, ProMash does the rest. Refractometer readings can be in either Brix, Zeiss or RI units (Brix is the most common measurement type for brewers).