A refrigerator's display shows the temperature of the air near its sensor, not the temperature of the food inside. A probe thermometer measures the food itself. The probe is pushed into the thickest part of the product, or between packs for packaged goods, and the reading taken once it stabilises. Infrared thermometers read only the surface, so they are useful for quick screening but not for confirming core temperature.
Probes need to be accurate and clean. Good practice is to check them regularly in iced water, which should read close to 0 °C, and to replace or recalibrate any that drift. Probes must be sanitised between foods, especially between raw and ready-to-eat items, to avoid carrying bacteria from one to the other.
A restaurant in Chandigarh might probe incoming chicken at receiving, check cooked curries during blast chilling, test buffet pans every hour and spot-check refrigerated stock at closing, writing each reading in the temperature log.