Don't waste your money on the Rheostat. I paid $19.99 for the Zoo-Med Rheostat and got a Zoo-Med Theromstat online for $23.00

The Rheostat was not low enough even on the LOWEST setting. I had to put cardboard between the UTH and the tank to get the temps down to a reasonable degree. Good thing I did not stick the UTH to the glass. It's not a good deal at all.