Specific Gravity Hydrometers for measuring the specific gravity of liquids heavier than water. All models are plain form, so a separate thermometer should be used to measure the liquid temperature (all hydrometer scales are based on 60° F. liquid temperature). Plastic hydrometers shown are fabricated from polycarbonate which makes them shatterproof, while still offering glass-like clarity for ease of reading. Manufactured and calibrated in accordance with NIST Circular 555 and ASTM E100-81. 12" long.