Mouse Clicks <<BR>> Button 1: Sets the cursor, drawing it in the new location, and marks the clicked vertex. <<BR>> Button 2: Sets the cursor without drawing it in the new location and unmarks the clicked vertex. <<BR>> Button 3: Clears marked vertices. Mouse Controls for Zooming <<BR>> Control+Button 1: Zooms in, doubling the zoom level <<BR>> Control+Button 3: Zooms out, halving the zoom level