This tool is used by Diesel Professional, Technicians and Operators to determine the overall quality of diesel fuel. The included "hydrometer float" will grade the fuel from 29-51 on the API gravity scale (keyword "API GRAVITY" if you are unfamiliar). The included "temperature correcting thermometer" will ensure consistently accurate readings. Checking fuel quality will result in better MPGs, cleaner burning engines and increased consumer awareness. Instructions included. Industrial Quality. Made in the USA!