ASTM 151H Soil Hydrometer is graduated to read specific gravity. It has a range of 0.995 — 1.038 in 0.001 divisions at 68°F (20°C). This hydrometer comes with a NIST-traceable certificate of calibration. 152H Soil Hydrometer measures in grams per liter (g/L) of suspension and has a range of -5 — +60 g/L, in 1g/L divisions at 68°F (20°C). It is also supplied with a NIST traceable certificate of calibration.