The Accurate Thermal Systems ThermCal400 Dry Block Temperature Calibrator is a small, rugged, portable and light weight calibrator that is easy to use straight out of the box with specifications good enough to be a laboratory standard. Perform calibration checks on liquid in glass thermometers, dial thermometers, hand held digital indicators, probe assemblies, systems and virtually dozens of other temperature monitoring and recording devices. Checking the performance and accuracy of a temperature sensor is best performed by placing it in precise environment at it's true operating temperature which is what Dry Block Calibrators do well. The included large multiwell insert has 5 holes to accept the more common probe diameters; 1/8 inch, 3/16 inch, 1/4 inch, 5/16 inch and 3/8 inch. Additional inserts with various hole sizes can be purchased separately. A blackbody source is also available as an insert that fits into the heater block, just like the standard inserts, using the insert extractor tool (purchased separately).