Last year I was sheathing a roof on a chilly November afternoon. It was cold enough that the nail gun I was using was slowing down a bit—the drive stroke and the return stroke of the piston were two distinct sounds. At the time I didn't understand why an air gun slows down when it's cold, and right then I wasn't too interested. The job kept me busy—at least until the drive stroke didn't return and I was left with most of the roof left to sheath and a gun spouting a steady stream of air. I finished the day with a hammer and fell short of the estimate. Afterwards, I expected to be working my