Reads actual specific gravity for an accurate measurement of battery sate of charge. Float type has built-in thermometer for temperature correction. Variation of .20 or greater specific gravity between battery cells indicates a need for battery equalization charging or a weak cell.
Dial Type Hydrometer 
Reads actual specific gravity for an accurate measurement of battery sate of charge. Float type has built-in thermometer for temperature correction. Variation of .20 or greater specific gravity between battery cells indicates a need for battery equalization charging or a weak cell.