Features and Benefits:Helps troubleshoot engine performance issues by testing diesel fuel;Tests #1 and #2 grade diesel fuel;American Petroleum Institute (API) gravity reading gauges diesel fuel composition and combustion characteristics;Quickly troubleshoot engine performance problems and measure #1 and #2 grade diesel fuel quality. The hydrometer measurements are given as an American Petroleum Institute (API) gravity reading when testing diesel fuel composition and combustion characteristics. Fuel is drawn into the hydrometer tube which then floats the internal bulb float. The internal float contains a thermometer that is used to compensate the API reading for the highest accuracy. Instructions included. Hydrometer Scale: 30 to 110. Correction Scale: +2.5 to -5.0. Applications include #1 and #2 grade diesel fuelsSimilar to OE tool #J-38641-D.