There's an article I posted on another thread about my problems with maintaining the temp in my incubator. I did have a better success rate when I switched out to a digital thermostat. Even though mine is a circulating air one, each tier has a temperature gauge that won't always match the one above or below it. You might want to invest into an infrared thermometer (the one that looks like a knockoff start trek phaser) and use that to actually measure the egg temp and not the air temp. I noticed, though, that usually the temp of the egg is always a little lower than the air temp (usually around 95-97 vs 99-101 for the air temp) The core egg temp seems to be very stable regardless of the air temp, barring any large fluctuations (did have a power outage the first time I was incubating for about 8 hours and they cooled off down to around low 90's).