My husband made me a styrofoam incubator and it fluctuates from 102 to 96 degrees. The person I got the specs form to make the bator said that it will fluctuate and to fill a kiddie cup with a lid with warm water and put a thermometer in there, this will mimic the inside of the egg. The temp on this should be 99.5. I have done this and my temp on the cup has stayed at 99.5 for days now.