Electro-optical display apparatus includes a plurality of modular units (M1-M4) each having a projector (5) for receiving electrical signals, converting them to optical images, and projecting the optical images via an optical projection system (18) onto a screen (4). The modular units (M1-M4) are arranged in a side-by-side array such as to produce a combined display on the screen. A calibration system detects distortions in the combined display caused by the projection system of each modular unit and modifies the electrical signals applied to the projector of each modular unit to correct the combined display with respect to the detected distortions.