the black thing is the temp probe I place mine on the heat source and tape it down then I set my johnsons control to allow for about a 93 turn on and shuts off at about 106 I done the temp checks and it give the bps a minium warm spot of about 93. I am planning on taping it in the middle of the tubs ( to prevent the rubbing effec I am seeing) and cut a busted tub up enought to figure out a inside temp with inbedding in the plastic so I can get a more true reading all the time. wit hmy flexwatt glued to the wood it heats the wood up and reflects it around into he tubs..