Incubator temperature variance

[13baker]

Hi, I'm new to the incubating game and still trying to get all the technical what to dos down. Anyway, can anyone tell me if I'm incubating eggs is the temperature the average temperature or does it need to be a constant temperature? I've tried to use a water heater thermostat and the high and low end of my temperatures vary more than I like. However, my average temperature when taken on one minute intervals through a heat cycle work out about right. Any thoughts?

 

[ducklover101202]

What does it vary between and your hatching chicken eggs,right?