SG is an automotive tester or handheld refractometer used to determine the specific gravity (sg) of electrolyte solution batteries as well as the freezing point of propylene or ethylene glycol-based coolants in degrees Celsius (°C). Maintaining the proper antifreeze concentration in an engine can prevent costly repairs. Thus, this tool is used worldwide by trucking and automotive technicians to ensure proper dilution. This refractometer works well for measuring cleaning products too. The instrument also gives indication of the charge level in battery acid.

The ultra-smooth focusing eyepiece provides high-quality optics, presenting an easy-to-read scale on a semi-transparent blue background. Ambient room lighting offers ample illumination to clearly read the results.