Hi,
Well that's the thing - I use an incubator even more basic ( see below for the ghettobator )than that and it holds closer temps.
How many waterbottles do you have in it for thermal ballast?
And you might be surprised the difference moving the probe from just sitting in the incubator to being inside the egg box itself or vica versa will make.
But yes you really do want to avoid those kind of temp swings if you can I think.
That is simply an insulated fish tank with a fish tank heater in the water which fills the bottom third and a shelf fixed above. It holds within one degree most of the time.
It does mean everything is as humid as possible - which can be both a good and a bad thing. On balance I'd prefer to build a more traditional incubator but I'm having trouble finding a glass fronted fridge.
dr del