Where do I place it? What is the best kind to use? I've always just watched the chicks and moved the light closer or farther away depending on their cues. Now I'm (hopefully) going to have hatchlings, and want to make sure they don't get chilled.
I set the thermometer directly under the brooder light. I usually set it on a scrap of wood so that it's right at chick height. Once I get a base reading under the light, I adjust the temp by raising or lowering the lamp (95F for the first week, lower temp by 5 degrees each week afterwards).
We got our thermometer from TSC for 2 or 3 bucks, its easy to read and also has a humidity gauge.