Click on a spot to create a start point for your line. Click on a second spot to create a line between the first spot and the second spot. Press space to use commands. List of commands: 'hidecursor' - Hide the red dot that indicates where the line will be drawn. 'showcursor' - Show the red dot that indicates where the line will be drawn. 'clear' - Clear the page. 'undo' - Erase previous line. Can be used as much as you want. You cannot undo the 'clear' command, though. (Shortcut - 'Z')
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