The Sper Scientific Batter Coolant Refractometer measures the freezing point of automotive coolants in their current concentration as well as battery charge

Both ethylene glycol and propylene glycol antifreezes can be measured, on separate scales. Battery charge is measured on a third scale using just a few drops of battery electrolyte solution (battery acid). The specific gravity of the battery acid is displayed together with a reading of RECHARGE, FAIR, or GOOD. To operate, simply place a drop or two of sample on the prism and read the results.