ZGR series has its own light source. With the built-in light source, it makes more convenient to use when in a Dark or Dim room or when doing wide-field work.And it also can use the outside light source to test. It is convenient to replace the batteries when they were use out.The models have only one unit system: °F. With the indication of the percentage we may know the freezing point of either ethylene glycol or propylene glycol based cooling systems.And they can also be used to test the concentration of ethylene glycol or propylene glycol in antifreeze liquids.The ZGRA-100ATC has Automatic Temperature Compensation System. Guarantee: Offer 2 years warranty Specification: Measuring Range: Ethylene Glycol: -84°F-32°F 0--70% Propylene Glycol:-60°F-32°F 0--63% Battery Fluids:1.100-1.400sg Resolution Factor:5°F,5°F, 0.01sg (ATC)Temperature Compensation Range:10°C-30°C Power Require: 3 “ " Button Cell (1.5V*3) Battery Life: More than 100hours Light Source: White LEDDimension: 27x40x160mm