I bought one (PepBoys - $50) a couple months ago since the temp gauge in the TR3 I had recently purchased was not working and it might be a while before I could either repair or replace it. At a distance of about 12 to 14 inches the target area is about 1 inch square. I aim it at the metal thermostat housing (I bought the meter with the laser pointer; accurate aiming is easier). You can take a reading off both upper and lower radiator hoses (they do vary), but the hose itself provides insulation. To check the accuracy of the handheld meter I put a pot of water on the stove with an egg in it and brought it to a boil. You need a target in the water as the bottom of the pan is in direct contact with the stove burner and will give a high reading. After a few minutes I got a consistant reading off the egg of 210 degrees...I was satisfied...and ate the egg.
Ray