M-duf, or Multi-directional universal foreshortening is a way to balance out your painting.

You can see it here in this piece. A flower was photographed several times from several angles. Then the insides were cut out from the outsides in the drawings. They were rearranged  and put back into the different flowers.

Now the outsides of the flowers look like they are angled in different directions and the insides are angled in different directions from the outsides.

This can be seen here, in the larger flowers. By doing this, a balance and control can be created that could not beforehand.

This is called M-duf.