Handheld refractometer to simply check the freezing point of radiator and washer fluids as well as battery acid to determine the condition of the battery. Measures both ethylene and propylene glycol. The refractometer is an optical instrument that measures the concentration of a liquid by means of its refractive index. Open the hatch and place 2-3 drops of liquid on the prism. Aim the front part of the refractometer towards a light source, and adjust the focus with the eyepiece and read the value. Easy to calibrate and adjust. The measuring range for battery acid is 1,100 (discharged)-1,400 (fully charged) kg/l.