Skip to main content

### 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.

### Comments

Dave O said…
Only things I can think of:

1) Some variation of Benford's Law is at play
2) The buttons were not all from the same batch during manufacturing. For example, maybe 1, 4, 7, 8, and 9 were made in a separate batch of differing quality, resulting in greater-than-usual wear than the numbers in the other batch.
3) The PIN is a hash value of some kind, and the hash function results in an unusually large distribution for the worn digits. Example: Geographic region of the customer might be encoded in the PIN, and perhaps a small number of regions are more popular than others.
4) If the screen's dialog uses digits to navigate the menus, perhaps those worn numbers reflect the most commonly selected menu items.
5) Similar to #3: If the bank is using common words as the basis for generating digits, then the resulting number sequences may reflect higher frequencies for common letters.
6) All the buttons were worn down evenly, but only some of the digits were recently replaced with new buttons. Or, someone smashed the buttons, and only the broken ones were recently replaced.
Confusion said…
I'm going with your option 6. ATM's attract a lot of vandalism.
Unknown said…
Another option is if 1, 4, 7, 8, 9 and OK tend to get pressed with the index finger, at least if you’re right-handed, and it causes more wear than the middle or ring fingers on 2, 3, 5 and 6.
Vinny Burgoo said…
Or people station their index fingers above the top right button, perhaps because that seems the best way of shielding the pad from prying eyes, and prod the numbers from there. Vertical and near-vertical prodding might produce slightly less wear than prodding at an angle.

Or something else entirely.
Alex said…
Or the Italians never fixed this little beauty?

http://www.theregister.co.uk/2005/10/21/phantoms_and_rogues/
sesqu said…
Was there a window nearby? Maybe the wear pattern was simply the summer sun hitting some keys.

### How to write a successful blog post

First, a quick clarification of 'successful'. In this instance, I mean a blog post that receives a large number of page views. For my, little blog the most successful post ever got almost 57,000 page views. Not a lot by some other standards, but I was pretty happy about it. Looking at the top 10 blog posts (by page views) on my site, I've tried to distill some wisdom about what made them successful. Your blog posting mileage may vary. 1. Avoid using the passive voice The Microsoft Word grammar checker has probably been telling you this for years, but the passive voice excludes the people involved in your blog post. And that includes you, the author, and the reader. By using personal pronouns like I, you and we, you will include the reader in your blog post. When I first started this blog I avoid using "I" because I thought I was being narcissistic. But we all like to read about other people, people help anchor a story in reality. Without people your bl

### Your last name contains invalid characters

My last name is "Graham-Cumming". But here's a typical form response when I enter it: Does the web site have any idea how rude it is to claim that my last name contains invalid characters? Clearly not. What they actually meant is: our web site will not accept that hyphen in your last name. But do they say that? No, of course not. They decide to shove in my face the claim that there's something wrong with my name. There's nothing wrong with my name, just as there's nothing wrong with someone whose first name is Jean-Marie, or someone whose last name is O'Reilly. What is wrong is that way this is being handled. If the system can't cope with non-letters and spaces it needs to say that. How about the following error message: Our system is unable to process last names that contain non-letters, please replace them with spaces. Don't blame me for having a last name that your system doesn't like, whose fault is that? Saying "Your

### The Elevator Button Problem

User interface design is hard. It's hard because people perceive apparently simple things very differently. For example, take a look at this interface to an elevator: From flickr Now imagine the following situation. You are on the third floor of this building and you wish to go to the tenth. The elevator is on the fifth floor and there's an indicator that tells you where it is. Which button do you press? Most people probably say: "press up" since they want to go up. Not long ago I watched someone do the opposite and questioned them about their behavior. They said: "well the elevator is on the fifth floor and I am on the third, so I want it to come down to me". Much can be learnt about the design of user interfaces by considering this, apparently, simple interface. If you think about the elevator button problem you'll find that something so simple has hidden depths. How do people learn about elevator calling? What's the right amount of