An apparatus for measuring temperature comprises a housing and an actuator pressure sealed to the housing and having a shaft. The actuator is configured to be in pressure communication with a volume of gas or liquid. Upon a change in pressure, the actuator is displaced at least partially in the axial direction. A sensor detects axial displacement of a magnetically encoded target upon the change in pressure in the volume. A device for measuring pressure and temperature in an engine cylinder comprises a valve in pressure communication with an engine cylinder. The valve stem has a magnetic coding located adjacent a sensor. Axial displacement of the stem under cylinder pressure and temperature changes are detected.