You would be talking about the proportional and non proportional mode. Proportional mode( dimming ) is a much more accurate way to power your equipment as it fluctuates the power going to the equipment keeping it at a nice steady temp.Usually in the tenths of 1 degree. while non proportional uses an on/off affect.Usually +/-2 or more degrees. The herpstats come with a setting that controls the " swing " of the temperature. I would definitely say that in a situation as delicate as an incubator, I would use the proportional setting without a doubt!