Brake Fluid Tester (Note:Just as the Custom problems recently,some orders can not pass the Security check as the battery,and many packages were retuned,as this reason,we remove the battery,if you need the battery,you can buy one in your local area.Hope you can understand that) To Check Fluid Quality: Press the button for power on, green LED will light up. Insert the tester into reservoir for a second , then the results will be indicated correctly by LEDs. Auto power off . Indications: Green: Battery OK, i.e.: No Water Contained in the Brake Fluid Yellow: Less than 1% of Water Content in Brake Fluid Yellow/Yellow: Approximately 2% of Water Content in Brake Fluid Yellow/Yellow/Red: Approximately 3% of Water Content in Brake Fluid; The Brake Fluid Should be Changed Yellow/Yellow/Red/Red: at least 4% of Water Content in Brake Fluid; The Brake Fluid Must be Changed Urgently, Extreme Danger.