A radiometer includes a sighting system that generates a digital image of an object surface having an area that is to be imaged onto the IR detector. A shape outline is overlaid on the digital image of an object surface to indicate the extent of the energy zone that is imaged onto the IR detector. A distance entering interface is used to enter distance data indicating the distance between the radiometer and the object surface and the distance data is utilized to determine the size of the overlaid shape.