The Series A4 digital differential pressure controller is a patented microprocessor based pressure controller for positive, negative, and differential pressure as well as velocity and flow. The Series A4 differential pressure controller includes (2) 8A SPDT relays and an associated programming menu that allows full configuration of variables such as setpoints, dead band, engineering units, flow coefficients, and more. The programming is done from a user friendly menu on the OLED display or uploaded using an Opti-Link™ programming key. The OLED also displays the exact setpoints or other user defined variables during normal operation. Furthermore, the menu structure can be customized by moving variables to different menu levels to accommodate many applications. Compared to other mechanical products, the Series A4 digital differential pressure controller has a significantly reduced depth, an improved look, and better performance at a similar price.