The Performance Tool W181 Brake Fluid Tester is the ideal tool for accurate moisture level determination in brake fluid, ensuring optimal vehicle safety. With a 5 LED readout, the results are easy to interpret, displaying the percentage of moisture in the fluid. The W181 Brake Fluid Tester comes with a 1-AAA battery, so you can use it immediately upon receiving it. Calibrated specifically for use with DOT 4 brake fluid, you can be sure of accurate readings every time. Even though it is primarily calibrated for DOT 4 brake fluid, the W181 Brake Fluid Tester can also be used for estimates with DOT 3 brake fluid. However, please note that it is not suitable for use with DOT 5 brake fluid. Stay safe on the road and make sure your brake fluid is in top condition with the Performance Tool W181 Brake Fluid Tester.