RE: Operating Temperature
An infrared temperature gauge can be a valuable diagnostic tool, but primarily for comparing from one day to the next. At least on a single cylinder engine.
As BillS said, in racing we used them to compare the exhaust temps from one cylinder to the next to check cylinder balance. And in this use, if you have a multi cylinder engine, a temp gun is really a good tool to have when setting the two (or more) cylinders to match.
Bill.