You're going to want to put in relative close proximity to your heat source. If it's a still air within a few inches of the heat source. Mine is a forced air and the heat source is in a separate compartment so mine is in the egg compartment a couple of inches from the diffusing vent that blows the heated air, works well with a 1 degree variation.
Well I have spent the last 4 days experimenting with just that issue. and tonight I think I found the answer. I will say I have found the best location so far. I am using a Water Heater stat with as much of the front carved out of it as I can get to expose the metal disk inside. I then mounted with the back metal plate toward the light and about 1 inch away from it. this makes the stat cycle about every 2 minutes. I am expecting this to hold the temp to about 2 tenths of a degree at most. I am waiting for the whole incubator to level out after the last bout of rebuilding and will know much more tomorrow. but for now I will say metal back to the light and close will give you low temperature fluctuations. I am not sure you even need the holes in the front this way but I am sure it does not hurt.
By putting the thermostat right next to the heat source....you wont know the temp further away from the heat source...it can be perfect right next to it....but further away it may be 2 or 3 degrees cooler.
Lyz, I have a total of 5 thermometers in the box. I just have the digital next to the thermostat to get an idea what temp it is turning in and off at. Not perfect but the best I can come up with at the moment. I work for a major University and they are planning on closing down the Ag Dept. No telling what sort of lab equipment will be going in the dumpster. Temperature sensors that can be placed on the exact surface you want to monitor. machines that will chart the temp second by second. heat sources that are not even very well known. Humidity generating equipment, filters, purifiers, monitors, pumps, you name it. they can take the fun out of anything. They hang stuff all over the walls labeled something like. "Factors in morbidity of tyrannosaurs Rex ranged on indigenous foliage" and then hang pictures around it of weeds soaking in laboratory beakers and what not. Never have understood much of the rest of it.
That is true, but whatever you set the thermostat for will keep the temperature constant. So if it's set at say 102 to 103 or more near the heat source it will still hold the temp steady near the eggs at 99.5 to say 100.5. I've found (at least with my incubators) that there's no way to get the tempearture perfect in all areas of the bator if you've got a happy medium of 99 to 100 degrees in the larger percentage you'll do just fine. But more to the point, the stat functions better nearer the heat source, but not too close.