7.4.4 Retention Factor

The Retention Factor was discussed in Sec. 5.2 on scrolling. It is the parameter used by the zoom operation to decide how much of the image to retain off-screen. For instance, if the retention factor is 3, only the middle third of the viewable area will be visible in the image area immediately following a zoom operation. In this case, think of the image area as the middle square in a 3x3 grid.