Ah yes; there is that!! However, you need to get a feel for the humidity inside the tub and so a sacrifice to the pee and poo gods needs to be made!!

I used to have one in every tub until I wanted to be like Kara and be able to 'feel' the correct humidity. Now I have one Acurite in one tub and play the 'How close to accurate humidity can I guess' game. I'm getting pretty good!!