Pieces of eight

For Christmas I bought Ben a book by Simon Singh called The Simpsons and their Mathematical Secrets. I think Ben is enjoying it because I’ve heard him laugh a few times, most recently this morning after reading this joke:

Q: What says “pieces of seven, pieces of seven”?

A: A parroty error. 

I didn’t get the joke because I’d never heard the phrase “pieces of eight” before but now that I understand it the origin of the phrase is quite fascinating. It refers to an old Spanish coin which was apparently the first world currency in the sense that it was internationally accepted and crossed borders. These Spanish coins were used all over the world and were legal tender in the United States right up until 1857. They were made with silver and highly regarded because the edging made them less susceptible to unscrupulous traders who would otherwise shave bits of silver off the edge.

The “pieces of eight” comes into play because the coin lent itself to cutting up into 8  wedges. This was useful at a time when there weren’t the different coin denominations we have now. Instead people took matters into their own hands and cut the coin when they wanted to give change or use smaller pieces. This was evidently perfectly legal.

** update **

I thought I’d better explain the joke. The pirate, Long John Silver, had a parrot that would say, “pieces of eight, pieces of eight”. The joke references “pieces of seven” which is the parity (parroty) error because seven is odd and eight is even.