The DM440 is a battery powered indicator for fitting directly to a Pt100 probe assembly or to be mounted remotely with an external probe, to display the temperature digitally. Sealed to IP67, the DM440 can be safely situated in the process area where hosing down is a regular event. Being microprocessor based, the indicator has certain "Smart" features, the most significant being automatic self calibration. During each measurement the resistance of the Pt100 probe is compared to a standard high stability resistor, the microprocessor calculates the temperature from the ratio of the two resistances. This means that both, the short and the long term stability of the instrument is determined by a single high accuracy, high stability resistor (PATENTED). The microprocessor also provides the ability to select the display to °C and °F by changing an internal link.