The Storage Battery Systems SBS-2003 Digital Lead Acid Battery Hydrometer tests specific gravity of a sample by inserting the nozzle into the battery and depressing the finger pump, which draws a few drops of sulfuric acid (H2SO4) through the tube. Within three seconds the measured refractive index is converted into a temperature compensated specific gravity reading and the temperature, specific gravity, and cell count are displayed. After testing is completed, data can be transferred to your computer via Bluetooth and the results downloaded into an Excel report.