I finished building my incubator (styrofoam cooler type) and I am having problems with the thermostat. It has about a 10 degree variance of when it shuts off and comes on. Does anyone else have this problem. I am using a hot water heater thermostat, a 25 watt light bulb, digital thermometer and a computer fan. Any ideas? I have a little time to tweak it. I want to put eggs in in February (21st).