Hey Cyndi, I test my thermometers by ice testing them, and 32 degrees means they are perfect. Anything above or below is how many degrees your thermometer is off by. Here's the link to the website I first used-
http://virtualweberbullet.com/testing-thermometers-for-accuracy.html
The boiling one is pretty hard, and the ice one is really easy. Just swirl the water around every couple minutes is what I do. Then I let it settle and read after a while. Hope this helps you, obviously you can't test the bator itself, but at least you will know if it's off.