about this item： Professional brake oil detection pen: designed to simply check the quality of brake fluid. Insert the tester into the tank for a while, then the results will be indicated correctly by lights. 5 LEDs indicate the result: 5 LEDs indicate the percentage of water in the brake fluid. A water content of 1% to 2% indicates the fluid can still be used, with 3% to 4% indicating you need to change new fluid for a safe ride. Change the brake fluid if the percentage is higher than 3%. Easy to use: Turn on the tester by pressing the button above. The green LED starts to light up. Hold the test sticks for a while in the brake fluid. Then the test result is displayed with the LEDs and the tester turns off automatically after 12 seconds. Professional tool: the tester can be used as a digital brake fluid tester suitable for determining the the quality of the brake fluid. Developed for professional use in auto repair and maintenance shops. Portable size: Small and light to carry for convenience, a great assistant for your trip. Detailed explanation of the meaning of the light luminous: Green: the battery is in good condition, i.e. there is no water in the brake fluid. Green / yellow: the content of brake fluid water is less than 1%, the brake fluid has good performance and can be used with confidence. Green / yellow / yellow: the water content of the brake fluid is about 2 %, the brake fluid can be used continuously. Green / yellow / yellow / red: the water content of the brake fluid is about 3%, it is recommended to replace the brake fluid.< br/> Green/Yellow/Yellow/Red/Red: The water content of the brake fluid is at least 4%, the brake fluid should be replaced immediately. Reminder: After each test, wipe the liquid part of the test point with a dry cloth or paper