## Wednesday, November 07, 2012

### The Rizzoli Conundrum

I was in the Rizzoli book shop in Milan buying The Economist when I noticed that the wear pattern on the pinpad used to pay using a debit card was anything but uniform.  Unfortunately, I didn't have my phone with me so was unable to snap a picture, but it looked like this:

There was heavy wear on the buttons 1, 4, 7, 8, 9 and the green OK button. The buttons 2, 3, 5 and 6 showed little wear. What could cause this?

At first I assumed that Italian debit cards had four digit PINs and people might be able to choose their PIN and use a birth year. To check that I grabbed the latest statistics on the number of people living in Italy by age (statistics are available from ISTAT in CSV format) and wrote a small program to process that. Based on people aged 18 to 80, assuming 4 digit PINs equal to birth year the wear pattern would be: 9 (29.08%), 1 (27.46%), 7 (7.39%), 6 (7.34%), 5 (6.39%), 8 (6.19%), 4 (6.13%), 3 (4.84%), 2 (2.70%), 0 (2.47%) (which isn't terribly surprising as there would have had to be a sudden drop in the birth rate in 1950s and 1960s Italy for the observed pattern).

Then I asked some Italians about their debit card PINs. Italian PINs are 5 digits long (not 4) and are chosen by the bank and cannot be changed.

So, can anyone come up with an explanation of what I observed?

PS If anyone's in Milan and can walk into Rizzoli and snap a picture of the pinpad (at the till straight in the front door) it would be cool.

If you enjoyed this blog post, you might enjoy my travel book for people interested in science and technology: The Geek Atlas. Signed copies of The Geek Atlas are available.

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