I am doing my first hatch in one now. I got extra thermometers and hygrometers as advised. I found the room temp, removed the large top thermometer dial and adjusted it to match what it should say. I did the same to calibrate the hygrometer. Then I switched it on and found that even then it did not stay accurate once the numbers started to climb. For the most part the temp gauge reads 5 degrees low and the humidity reads 10 degrees high. I am doing a version of dry hatching and will not have my vent plugs in at all so I run the hygrometer probe down through the vent holes. I also punched an extra hole right in the center where I was using a basal body digital thermometer and running random checks. But the batteries ran out and I nearly fried my eggs because I believed the readings on it. So far it seems to hold temp fine. I am not adding water so no idea about humidity. I am using an LG still air as a hatcher since I have a staggered hatch going. The little stick thermometer on a plastic card that came with it was way off and changed the degree by which it was off depending on how hot it actually was. I tossed it. So far I am on day 15 of Batch A and I had 20 of 24 make it this far. 2 were non-fertile and 2 had blood rings and looked like they died about day 3. Batch B was 17 eggs and is on day 12 - most were shipped Welsummer eggs. 3 were not fertile and 2 were scrambled in shipping. But right now my FI Pro 4200 is delivering 32 of 34 fertile eggs. Still have a ways to go and I am adding a batch C on day 18 when I transfer Batch A to the hatcher. So we will see how they all do! I got mine at Tractor Supply Company here in Texas for about $125.