Square Indian Coins? Huh?

I was looking through my Indian coin collection today and thought I'd take a look at this coin, and give it a good research!

This is a 2 Annas from 1944. 2 Annas is 1/8 of a Rupee. The coin is Nickel-brass and weighs 5.74 grams. With a diameter of 25mm it's not a small coin, nor too overpowering. What strikes me about it is the shape! Square?! Fantastic.

Research that I carried out suggests that they used to have triangle, square, hexagon and octagon Indian coins. This was because most Indians were illiterate. If all coins were the same shape they could get confused. Is this true?

It sounds like a brilliant idea if it is. I couldn't think of that!