measuring temp of fermentor

how do you measure the temp of the beer in the fermenting bucket? my kit came with a thermometer that adheres to the outside of the fermenting bucket, but if you have the bucket in a swamp cooler or something, wont the thermometer on the bucket be altered by the ambient temp of the cooler instead of whats inside the bucket? or do you just keep tabs on the ambient temp outside the bucket and just assume the beer is a few degrees warmer inside?

thanks!

I havent seen these thermos as i am farely new but i have aquarium experience and it sounds like its a lot like an aquarium thermo. These stick on thermos usually have the temp readers on the sticky side and the face of the thermo is usually a form of insulation from ambient temp. These thermos still are not very accurate as the temps still have to go through a material like plastic or glass but are usually +-2° from accurate. Again this is what i know about aquarium stick on thermos not surs if brewing ones are the same or not.

I use the strip thermometers, like the aquarium ones, on my glass carboys. I'd be leery of the temp on a plastic bucket, the plastic is a good insulator. But I only brew in the glass, so don't have direct experience.

Yeah not sure how acurate it would be in such a low ambient temp. Maybe go to a fish store and ask them otherwise for a few bucks you can get a large glass thermo from you LHBS.

I use one on my plastic buckets and it seems like it works just fine. It was reading ~66F on the strip, and when I took my hydro sample, I stuck a thermo in it and it was at 67F. This was in a homemade swamp cooler also.

Strip thermometers on plastic buckets have been working great for several years here...

I dont have a floating thermo its a big glass tube thermo with black granules on the bottom by the mercury bulb amd it sinks into my wort so i am able to read the center temp were it would be warmest after the cool down been pretty accurate to my furnaces thermostat so far always reads about the same maybe a 1° variance if that even