This precision temperature gauge replaces the original oil filler plug and lets you keep an eye on the important motor oil temperature. It is important to remember that the water temperature does not indicate the oil temperature, they can be quite different. To keep the needle steady the instrument is filled with a damping fluid, the air bubble left is to allow heat expansion. The gauge provides accurate reading, the "Tourenfahrer" motorcycle magazine test results say: "... The accuracy is very good... and is definitely worth it's cost". The outer ring provides a solid grip and makes installation and removal easy.