I'm working on my soldering technique and I'm having trouble getting a reliable indication of the joint temperature with my IR thermometer. It's a Kintrex IRT0421, and it has always delivered what seemed to be accurate measurements in the past. Now, if I use it as a "forehead" thermometer, it gives me a reading within reason, but if I try to measure the temp. of a soldered joint, or even the temp. of the functioning soldering iron, it gives me a figure lower than human body temperature, e.g., 77.5˚F. IF I point it at the space heater, I get a believable reading, but if I switch to the soldering iron, I don't. What am I doing wrong?