The brake fluid test pen is used to test the quality of brake fluid. The brake fluid water content percentage test result is displayed by the number of 5 LED lights on the test pen. The FT123 brake fluid test pen measures the moisture content of brake fluid based on changes in conductivity and clearly displays the moisture content through a light-emitting diode. High moisture content will cause the boiling point to drop, affecting braking performance. A red light indicates that the brake fluid needs to be replaced, a green light indicates that the brake fluid is in good condition, and a yellow light indicates that the condition is acceptable. Performance characteristics Powerful functions, simple operation, precise measurement, use safe;Detects all brake fluid; has an auto shut-off feature; Can test DOT3/4/5 brake fluid. Product Instructions Green: power OK/no water; Green/yellow: moisture content is below 1%; Green/Yellow/Yellow: Moisture content close to 2%; Green/Yellow/Yellow/Red: the water content is close to 3%, it is recommended to replace the brake fluid; Green/Yellow/Yellow/Red/Red: The water content is more than 4%, dangerous, and the brake fluid must be replaced immediately. Note: The above data is only for reference; Battery: 1 AAA battery, not included Note: The data is all measured manually, please allow 1-3cm error, due to the difference in light and display, there will be a certain color difference, the actual item received shall prevail.