This control drop the vacuum pressure when the temperature decrease or increase if the temperature rise. This methode is used to avoid a freeze pipes, so the lower vacuum is, the minimum freezing are inside the pipes. The adjustements are quite simple and pretty efficency. Also, You can start the vacuum pump whit temperature (trim two pots inside the enclosure)  plus it's possible the get a hight limit protection against a water come in the vacuum line.the controller come with 10mm proportionnel valve and pressure transmetter