The EZRED DEF Hydrometer, No. SP110, is ideal for quick, accurate, and easy-to-read level readings of diesel exhaust fluid. The DEF tester uses a proprietary method to provide accurate results and even compensates for temperature. Simply draw the DEF solution into the hydrometer, tapping away any air bubbles. If the arrow is in the ‘good zone’ the solution does not need to be replaced. If a longer reach is needed, users can attach the included extension hose by inserting the smaller tip into the attached hose. The SP110 is made in the U.S.A.