TelTru is a premier manufacturer of replacement thermometers; various of us have several (trading sensitivity for range). They state a low temperature operating limit of -50F for bimetal thermometers with silicone fill. My speculation is that their other bimetal thermometers have no such lower limit. The display quite naturally goes off scale low well before this point. Whether this causes loss of calibration is both an empirical question and a question for each manufacturer. My thermometers often see 25 F over winter nights, and on low & slow cooks the comparison with my BBQGuru is at least a sanity check (the different locations take a very long time to converge to the same temperature, even if all instrumentation has perfect accuracy). So, dunno. I've been able to ignore this issue and my food tastes good. As I said, ultimately an empirical question. Who has witnessed loss of calibration after freezing nights? For the regulation issue, the operating temperature range would be a good question for Dennis to take up with his supplier. Don't get me wrong; I deeply respect asking this question. What's the poster child for asking this question? Apollo 13 returning home alive after a severe explosion in space. The ultimate cause of the explosion was bare wire inside an oxygen tank, which sparked the contents during a routine in-flight stir. Earlier on the ground, NASA needed to boil off the contents of that tank, missing a voltage design change that accidentally fused a heating element always-on. They asked some guy to sit on a folding chair and say something if a thermometer read over a certain limit. The thermometer quickly reached and got stuck at this limit; it wasn't designed to read off scale high. The guy didn't say anything, and the tank problems went unnoticed. Did he fall asleep lol Sent from my SM-P600 using Tapatalk