It looks like the temp reading is on the end of the probe, how do you check it without opening the incubator. Are you using a glass bottle or plastic? It looks glass. Very good idea, BTW
Even if the bottle is the size of a peafowl egg, wouldn't it register the same for a guinea or chicken egg? Or is the size a big difference?
Someone posted how to make a water wiggler using 2 ziplock bags, a couple of rubber bands and a probe from Walmart but I think it would be the same possible problem, the size of the eggs vs the baby bottle or ziplock bags.
Don't make one. They leak. Just invest in a probe that fits in and runs out of the incubator. I think I paid $7 on amazon. I couldn't find mine but I did come across this. one about the same.
http://www.amazon.com/Portable-Digi...&sr=8-13&keywords=aquarium+digital+temp+probe