You can check the accuracy of a temperature sensor by placing a calibrated reference temperature sensor (not supplied by Huber/Radleys) close to the sensor in question, and noting the readings at your desired temperatures.
If you would like to calibrate an external temperature sensor (a Pt100 you have purchased as an optional accessory, to plug into the Huber (via the LEMO socket) and position in your application (e.g. jacketed lab reactor), you can simply place your calibrated reference temperature sensor next to the external Pt100 in the application.
Huber units contain an internal temperature sensor, which is used to measure the temperature of the thermal fluid flowing out of the Huber unit to the external application. Please note that Huber calibrate the temperature sensors at their factory, and so calibration of new units by customers is not required. Nonetheless, if you would like to calibrate the internal temperature sensor, to position your reference temperature sensor next to it, you would need to purchase a calibration bend.
The calibration bend would be mounted on the Huber outlet, and has a sensor pocket for inserting the reference sensor. There are different types of calibration bends, for different sized Huber fittings and sensor diameters. (It is not possible to remove the internal sensor from the Huber unit to calibrate it.)
If your Huber unit has a Pilot ONE controller, you can then offset the current temperature reading to match the reference temperature. Navigate to Menu → System Settings → Sensor Adjustment.
With Professional or Exclusive levels (E-grades) of the Pilot ONE software, you can calibrate 5 points (5 different temperatures); with the Basic software, a 2-point calibration is possible.