I have two digital thermometers and decided to check the accuracy of them, the question was how? Common sense told me to get a pot of water to a boil and see what they read. Good roiling boil and one read 210.5 and the other read 210.7. I know different sea levels affect the temp. of the boil and I'm only about 300 ft. above sea level, am I doing this right? How do you check yours?