I used to use one of these but found it far more accurate to get a cheap digi thermometer with a couple of probes so you can measue the cool and hot temps accurately.
I think most people stick the Fluker's type thermometers onto the side of the viv however this will only measure the surrounding air temp not the floor temp. I assume placing it on the substrate will measure the ground temp, it might get moved around by ur snake though.
:cheers: