Make straight lines?

[RobertF57]

Is there a way to ensure that the lines you make with the Line Tool are straight? When I try to draw a straight horizontal or vertical line with the tool using my track ball, my hand sometimes shakes which throws the line off causing me to have to delete and redraw it. I believe that with Visio you could hold down a key which ensures that the line is drawn straight. It would be nice if OmniGraffle has this feature.

Thanks.

[Lizard]

Hold down shift while you're dragging. This will constrain it to horizontal, vertical, or 45 degrees.