Quality is tested and indicated on five LEDs in terms of “percent of water in the break fluid” Battery(incl): one 1.5V,type AAA Tester Indication Green: Battery OK, no water contained in the break fluidGreen/Yellow: Less than 1% of water content in break fluidGreen/Yellow/Yellow: Approx 2% of water content in break fluidGreen/Yellow/Yellow/Red: Approx. 3% of water content in break fluid.Thebreak fluid should be changed.Green/Yellow/Yellow/Red/Red: At lease 4% of water cintent in break fluid.The break fluid must be changed urgently!Extreme danger!