F uses his calipers quite a lot, much to my surprise! He has found out all sorts of neat stuff that way.
Those are great to point at ceiling vents where air conditioned air enters the room, when it is hot in the house. It helps in figuring out if the air produced by your AC unit is as cool as it should be, or if the AC unit isn't working properly. F has one of those, too, and used it to help convince me that it was time to call the AC guys during a very hot September in 2016 when my house just wasn't as cool as I wanted. It turned out that the AC wasn't producing cool air, and I needed to have my entire AC system replaced.