The Herpstat displays a different temp than my equipment.

Question: 
Why is the temperature on the Herpstat different than when I check with a Infrared Temp Gun (or other thermometer)? 

Answer: 
Infrared temperature guns and cheap digital thermometers are typically not accurate enough and can be misleading when comparing them to the temperature reading from a Herpstat. Temp guns also only take surface temperature and do not account for air temperature around the standard probe. This is often confusing and not a good way to check if the thermostat probe is accurate. Most temp guns and digital thermometers have a accuracy rating of +- 2 full degrees. If your actual temperature was 90 degrees these devices can show 88 all the way to 92 degrees and still be considered "accurate". In my testing I have purchased loads of these by different brands and its rare that any two show the same temp. The sensor in the Herpstat probe's are +- .9 of a degree. It also has much finer resolution (steps that can be measured) than most other sensors. So in that same scenario the Herpstat probe could show 89.1-90.9 and still be considered accurate. This is much more precise. If you were to compare the two and the sensor on the thermometer was in its high end of the range and the Herpstat sensor was in the low end of the range you would see 89.1 from the Herpstat and 92 degrees from the digital thermometer and both devices would still be correct. The Herpstat probe's sensor is digital. This means the accuracy of its readings are not affected by voltage changes, wire resistance, ect like most other temperature sensors. We do not do any calibration to the sensors as they have calibration mappings recorded into them from the semiconductor company who manufactures them. Even with that we do pretest them. Typically they are plugged up and the readings are compared to 3 other probes over a short period of time. If any one is too far off then it alerts us. It is very rare that we find one that is off. In fact its been several years since I had to discard one for a invalid reading. 

The easiest way to verify temps is to take a couple of digital thermometers and tape their probes to the Herpstat probe and let them dangle off the side of a table in the air. Be sure that there is no heating device connected to the Herpstat during the test. Let them sit for 30 minutes and check the results. You should get some idea if there is failure but you will have to choose which temperature device you feel is the most accurate. Newer Herpstat models do have a sensor matching option that will pad its reading to match other equipment.