When testing if your meat is cooked, the coldest part will be the very centre of the thickest portion. Likewise, when chilling food, the thickest part will be the last to cool. When testing larger food, taking multiple readings from several areas will determine if the entire portion is done. Keep in mind that different types of thermometers have different sized sensors. A dial thermometer can have a sensor as big as an inch long with your temperature reading being an average of all the materials the sensor is touching. Most digital thermometers have small sensors at their tip, making it important to ensure when penetrating the food that the tip is touching the right area.