I'm thinking here that Vaughn's idea is likely the way to go. Do you have a reading on the room the rack is in because no matter what you do you have to consider that part of the equation. I have an old Acu-Rite that accidentally lost it's probe stuck up on the wall of our BP room. It's really helpful to know what the room temps and humidity are as I figure you can only fight the ambient room temps/humidity so much till you have to start thinking about adjusting that first.