One of the potential advantages of a digital thermo-hygrometer is that instead of sending the entire unit out for calibration, you can simply swap sensors and send only the sensors due for calibration out of the lab. The 1620A "DewK" Thermo-Hygrometer allows you to swap sensors without shutting it down or discontinuing your other readings. Smart sensors make this possible because all of the calibration information is contained inside the sensor. Your costs are reduced because the 1620A never needs to be calibrated since it is only a display. Spare sensors like the 2626-S are less expensive to store, ship and recalibrate than an extra chart recorder. The 2626-H is a spare high-accuracy smart sensor for all models of the DewK Thermo-Hygrometer.