>An edge of 100 from X to Y means "move 100 from X to Y", which is the same as "subtract 100 from X and add 100 to Y"

I think this is a perfectly succint explanation for people who have trouble grasping the double entry system. Because they are usually stuck thinking in terms of "move 100 from X to Y". And its hard to get them to think in terms of "subtract 100 from X and add 100 to Y".