Moisture in your brake fluid will give impaired performance and can be dangerous. This simple tester will check the percentage of water in your fluid, indicating when to replace it. Gunson 77002  Brake Fluid Tester is a simple and effective tester shows the condition of the brake fluid with a coloured response. - Test percentage of water in the brake fluid - Immerse the probe end of the tester into the brake fluid - use regularly for brake maintenance - Green indicates - Yellow indicates 1.5>3%water = marginal - Red indicates 3%