Multiplying with straight lines

While learning the Japanese abacus, you can't help becoming fascinated with numbers and arithmetical tricks. Here's a simple Japanese method of multiplying using intersecting straight lines 

Let's take 123 x 332 as an example -

Draw parallel lines in groups representing the number 123

123

Then draw intersecting lines to represent the number 332

123332

Now, separate the groups of numbers as illustrated and count the intersections in each separate set123x332

You get 3  9  17  13  6

Knock off the 10 of 17 and add it to the 9 on the left. Knock off the 10 of 13 and add it to the 7 on the left

Now you have 3  10  8  3  6

Again, knock off the 1 of 10 and add it to the 3 on the left

Answer 4  0  8  3  6

There are additional techniques, such as using a broad line to represent 5, but the principle remains the same. See if you can figure out why it works!