Brake Fluid Tester monitors the quality of brake fluid for the car owners; This pen-shaped brake fluid tester can easily help you to determine whether it is time for you to change your brake fluid. With compact portable design; Easy and quick way to test for water content in the brake fluid LED indicators lights show the percentage of water in the brake fluid; Only takes seconds to know the results. The included LED lights will indicate the percentage of water in the brake fluid: Green: Brake fluid is ok/Battery is OK, i.e.: no water content in the brake fluid Green/Yellow: Less than 1% of water content in brake fluid Green/Yellow/Yellow: Approx.2% of water content in brake fluid Green/Yellow/Yellow/Red: Approx. 3% of water content in brake fluid (The brake fluid should be changed) Green/Yellow/Yellow/Red/Red: At least 4% of water content in brake fluid (The brake fluid must be changed urgently, extreme danger!)Read for Brake Fluid Test: Unscrew the lid of the brake fluid reservoir, and take off the cap of the brake fluid tester. Dip the test probes into the brake fluid up to the plastic rim of the deviceTo Check Fluid Quality: Press the top button for power on, the green LED lamp will light up; Insert the tester into reservoir for one second, and then the test result will be correctly indicated by LED lamps (The tester will automatically power off after 12 seconds of inactivity)