If multi-stage control is required one or more stage modules can be hooked up easily to an A27 temperature control module, simply by using the included quick connector. There are two types of stage modules available: * modules with their stage setpoint linked to the thermostat setpoint. The stage setpoint can be set for the number of degrees of offset of the A27 temperature control module setpoint. * modules with independent setpoint setting. These modules act as a thermostat but no additional sensor is required.