It is best to insert the thermometer under the leg into the meatiest part of the thigh. Make sure to avoid bone and gristle, as the temperature will read higher than it actually is. When the thermometer registers 180°F in the thigh, insert the thermometer a little further in. If it registers lower, then allow it to cook until it reaches 180°F. If it does not change, then it has reached the proper temperature and is done.