Hand-Held Refractometer  - Battery/Antifreeze/Cleaning Fluid

The Hand-Held Refractometer For Battery/Antifreeze/Cleaning Fluid
  series are designed for measuring the concentration of the battery fluids. the freezing point of antifreeze liquid and windshield cleaning fluid. With the indication of the percentage you may know at which temperature the fluid will be frozen for both propylene glycol and ethylene glycol.

It can also be used for checking the strength of electrolyte solution battery.