Why do people say "PIN number"?

Answer by  tamarawilhite (17883)

"PIN number" is used because PIN is the common abbreviation for "personal identification number", but PI number could be mistaken for the number Pi. In a financial transaction, the clerk is rewarded for short cycle times. Thus they may simply say "Enter your PIN number" instead of "personal identification number" because it is quick and easily understood.

Answer by  ken65 (128)

I've often wondered about this but I think it just provides additional clarification than saying "PIN" and sounds better than 'PI Number"