Turn the thermometer on and make sure the reading is at zero

Slip the tip of the thermometer into a disposable plastic sleeve. Available at drugstores, these sleeves are usually a onesizefitsall product. Internationally agreed temperature scales are designed to approximate this closely, based on fixed points and interpolating thermometers. The most recent official temperature scale is the International Temperature Scale of 1990. It extends from 0.65 K to approximately 1,358 K .