Flat spring drive system and window cover

A spring drive system for window covers is disclosed, which includes a so-called flat spring drive and the combination whose elements are selected from a group which includes (1) a band transmission which provides varying ratio power transfer as the cover is opened and closed; (2) a gear system selected from various gear sets which provide frictional holding force and fixed power transfer ratios; and (3) a gear transmission which provides fixed ratio power transfer as the cover is opened or closed. The combination permits the spring drive force at the cover to be tailored to the weight and/or compression characteristics of the window cover such as a horizontal slat or pleated or box blind as the cover is opened and closed.