I built my chest freezer fermentation chamber with a STC-1000. For the first couple of months I was often suspicious as to whether the temp on the display was true to reality, so I would often pull a sample and check the temp. After doing that a number of times, I determined that the temp controller was reading accurately. Since then I don't really monitor the temperature. Although, every once in a long while I will check the temp of a sample to make sure that the temp controller is still working properly. FWIW, I also tape the probe to the side of my fermenters with a thick piece of insulation.