EPA regulations require all diesel engines manufactured on or after January 1, 2010 to meet lowered NOx emissions standards. Most heavy duty engine (Class 7-8 trucks) manufacturers, have chosen to utilize SCR. This Includes Detroit Diesel (DD13, DD15, and DD16 models), Cummins (ISX line), PACCAR, and Volvo/Mack. SCR-equipped engines require the periodic addition of Diesel Exhaust Fluid (DEF, a urea solution) to enable the process. DEF is available in a bottle from most truck stops, and some have installed bulk DEF dispensers near the Diesel Fuel pumps. However, to ensure the proper operation of the SCR system, operators must ensure the DEF in their vehicle consists of a 32.5-percent Urea / Water solution. The OTC 5025 makes this a simple and quick process for an operator or technician. Scale: 0.5-percent line graduations 32.5-percent Indicated Scale 15-40-percent Waterline and 20 Deg C Kit includes: Refractometer, dropper, lens wipe, cloth, instructions and quick guide, screwdriver and case.