Usually a thermoter is calibrated using an ice water mixture. Obviously not practical for an incubator, or the little electronic jobs. If you have an oven style quick read digital probe thermometer (and you should if you cook), you can insert it thru the the hole for humidity control and get a...
Set your thermometer across the two yellow bars if you can, so its at the same height as the middle of the egg (roughly). And I've seen mixed reviews on accuracy - I probably should have recalibrated mine before starting up this season
Mine looks just like that, but FAR dirtier. Don't worry about my recent bad hatch - I'm about 100% convinced its due to my placing it in the barn in the first place. And yes, its a very hands off thing, though maintaining humidity can be a bit persnickety, at least if you live essentially...
Tip. Take a permanent black magic marker, and mark the flat side on the white toothed "wheel" that moves the yellow egg divider around the circle. Do the same thing on the flat side of the metal pin that turns it. Now much easier to put the two together without sipinning things back and...