Some interesting ideas thanks, but probably a bit OTT/Technical and unfortunately some card drivers don't return a reliable scanline position, if any. Skidracer came up with a fix for tearing in windowed mode when using Graphics() (it's not perfect on some systems though) but others have been suggesting using a MaxGUI canvas instead of Graphics() for windowed mode and changing to event based programming. I just wondered if such a canvas does or does not show vertical tearing. If not then, it's a persuasive argument for using MaxGUI.