Baumé hydrometer, named for the French chemist Antoine Baumé, is calibrated to measure specific gravity on evenly spaced scales; one scale is for liquids heavier than water, and the other is for liquids lighter than water. Scientific Salt Hydrometers measure sodium chloride or calcium chloride. All have an accuracy of ±1 subdivisions Note: Hydrometers should be stored in a clean, dry, safe place, and should not be subjected to extreme temperatures.