The OTC 4598-DOT4 helps you catch bad brake fluid before it has time to destroy expensive brake calipers and other brake system components. It determines the quality of brake fluid and measures moisture from 0%-4%. Features LED lights to show moisture percentage, and automatically shuts off after 12 Seconds. 1.5V AAA battery included. Usage Instructions: 1) Remove cap from brake fluid reservoir; 2) Remove probe cap from brake fluid tester; 3) Press power button on top of tester. Green LED lights up; 4) Dip entire length of metal probes into brake fluid; 5) After one second, match color of LEDs with color chart to determine brake fluid quality. Tester automatically powers off after twelve seconds of inactivity.