Good morning;
Interesting topic and tangential diversion.
Brian Shaw made a comment about professional chefs having an intstant reading thermometer with them at all times. There was also something mentioned about salmonella, et cetera.
I think the main reason why the chefs carry a thermometer is to be able to have a ready defense when the Health Department Inspectors show up. Many of those guys do not really know that much about cooking and food preparation, so they "go by the numbers" and "I'm just doin' my job, man." They are told that the food must be brought up to "yea, that much" in temperature, so they watch the numbers. That is easier than trying to train the inspectors in recognizing what different foods look like when they are done.
On the subject of the original question, I agree that it is easier to just get another thermometer that is clean and designed for cooking.
My favorite developing thermometer was a yellow scale glass/mercury laboratory type specially provided for photographic purposes that read from about 18 degrees C to 32 degrees C and was calibrated in 1/10 of a degree C increments. That was back in the 1960's. Probably illegal by now.
Enjoy;
Ralph Javins