I have one. I have been using it with great success for about 40 years, it was given to me as a child, and it was 50 year old then. The weird looking thing in the middle is a mechanical switch...it expands with heat and in turn presses a microswitch, which turns a light on and off to maintain the desired temperature. It is accurate to the degree.The cool thing about it, is you can take that temperature switch put bigger lights in, and make a way bigger incubator with it. Keep that gem.. oh you put a pie plate of water under it to maintain humidity as well.
Regards
Chris