A temperature measuring device should be placed in the "warmest" area of the refrigerated holding unit. The reason for this is because all foods must be stored in the minimum temperature required. If not stored properly the foods become hazardous. It is important to place the thermometer in the accurate location in reference to this question it is in the warmest location. The reasoning behind this is that if placed in the coldest location it may not represent an accurate temperature based on the entire unit.