Abstract: A controller is disclosed for use in controlling environmental conditioning apparatus such as heating and air conditioning equipment in a building or the like. The controller is flexible in that it can control most types of such control devices and apparatus and it eliminates the necessity of a conventional local controller while permitting the use of a centrally controlled automated system if such is desired. The controller is self-contained in that it preferably has a display and keyboard for establishing and changing the operational limits of the apparatus that is to be controlled. Only one sensing device is needed for each apparatus that is controlled, since the signals that are generated by the sensing devices are compatible with the controller as well as with a central automated system if such is used. The controller eliminates the need for a conventional local controller for each apparatus and permits one controller to be used in conjunction with a plurality or a group of control devices.