I just picked up one of these units. I couldn't resist the sale at $19. Lots of uses around the house at this time of the year in finding air leaks, and checking out the cooling system on the old car. Can anyone shed some light on the theory behind what makes it work. I know that it measures the electromagnetic radiation coming from the surface aimed at to determine the temperature. I don't see how it works when the object surface is made of wood. Any takers?