I really enjoyed this thermometer when I received it. It doesn't stay completely stationary if you let it free float and there's enough current to budge it, but if you have substrate you can dig a little hole to let it sit in no problem. Since it doesn't have a suction cup, you won't have any suctiony residue you usually get from those on your tank... and because it's weighted at the bottom it doesn't float to the top and it also doesn't become inconvenient because it "lost its suction ability" like all the ones with the suction cups do. The only reason why I'm giving it a four star is because I broke my last one (it's actually not very easy to break, but my hand hit the thing REALLY really hard- and the fact that it IS breakable it is still a mild deterrent). The fact that they did so well reading the temperatures accurately and since I like them more so than the ones that you stick on the outside of your tank or use a suction cup with, I've actually bought two more for my two tanks. If you're looking for a cheap thermometer then this one is up your alley as it's affordable and convenient for your tank, as well as yourself!