Alternative Multiplication Method

http://upload.wikimedia.org/wikipedia/en/0/05/Gelosia_multiplication_45_256.png

I dont get it.

Here's a another method it's similar to the Lattice one; I dont know what it's called http://i43.tinypic.com/dw5lrr.jpg

It's meant to be 21 x 3 something. Apparently it's really quick and easy to do in your head ergo very useful.