LINEdesign draws using the PROforma graphics libraries. Drawings are actually produced in rendering buffers, which are then copied to the screen. However, when very complex drawings have to be shown, it might take a while before the picture is copied to the screen. To remedy this problem, the resuls is occasionally previewed. Doing this too often would slow things down, so the display has to appear a trifle sluggish.
In theory, it should be possible to draw everything to screen immediately, but expirience has shown that this can result in system crashes if you accidently move the mouse during some of the more complex drawing operations.