The kids and I built an incubator and have got 9 eggs sitting at days 16 and 17. We know for sure that 7 are developing, not sure about the other 2 because the shells are to thick, but air sac is getting bigger. We have been on a roller coaster because the temperature keeps rising and falling, so we have no idea of we will be ending up with birth defects or not. Anyhow we would like to try again but need some recommendations for a thermostat which will hold steady and will not break that bank. We tried an $8.00 hot water heater tank heater that my husband picked up at Home Depot but that also fluctuated. Any suggestions?