My normal incubating thermometer is an old alcohol one, (the kind with the red liquid in them) an indoor/outdoor weather temp type thermometer. The metal frame is all bent where a dog chewed on it years ago, but it works great. The only problem is it doesn't show 1/10th increments, so I have to just kind of eyeball it and make my best guess where the line should be. I always test run for at least 24 hours before setting eggs, an double check with the mercury shake-down thermometer. That also allows me to verify that I'm looking for the right spot on the alcohol thermometer. One of these days, I'll have a fine-tip sharpie handy when I test it, and I'll mark where the line should be. Or better yet, both ends, the high and the low, of the acceptable range.