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I am moderately pleased to have written one of the featured comments on a recent Daily WTF post. So what piece of programming wisdom has been recognised in this way? Which of my insights into the nature of computer science have I properly applied to the situation described in one of these humorous articles?

As if. In fact, the post in question was a matter of trivia, and my comment was also such. Mr. Papadimoulis expressed surprise that we British have a seven-sided coin (little did he know we have two), and I replied to let him know that not only are the coins in question (20p and 50p) seven-sided, also each coin has curved edges, to ensure that they have constant diameter. This property is very important for the manufacturers of coin sorters, vending machines, fruit machines, &c. It's also why you don't get eight- or six-sided coins: you can only pull the trick off with regular polygons with an odd number of edges.

In fact, before the Euro someone had an eight-sided coin. I'm pretty sure it was one of the French franc coins, but I don't have a copy of one nor can I find a picture, so I have no way to convince myself or you. Anyway, to accommodate this constant-diameter property, the traditional eight-sided shape had been inscribed into a circular coin.

Someone else, of course, mentioned that having non-circular coins is very useful for the blind, who want to be able to identify them by touch, and followed up by complaining that all the Euro coins are round. He didn't mention, so I will do so here, that in fact the Euro coins can be distinguished by touch because of their distinct milling patterns.

Milling is the pattern, usually of thin grooves, inlaid into the circular side of the coin (i.e. the side that is neither heads nor tails). It was originally introduced to stop people clipping a piece of gold off one side of the coin and passing it off as a full-weight coin, back when coins were actually worth their face value. This practice was so widespread that the Sterling nearly collapsed because of it, until Isaac Newton introduced milling (along with new, more efficient, minting techniques) at the Royal Mint, and brought a law before Parliament (he was also MP for Cambridge University at the time) making it illegal to use the old coins for any purpose other than paying debts to the King.

Anyway, since John Law (a Scotsman and one of the best candidates for richest man ever) invented the fiduciary (i.e. not backed by gold) note and with it the idea that currency didn't have to be worth its face value, this use of milling stopped being appropriate, but, as I say, it is still useful for allowing you to count your change without taking it out of your pocket.

The €.01 coin has no milling, like the Sterling copper coins.

The €.02 coin has a groove running circumferentially, all the way around the middle of the circular side. This feature is actually quite annoying, as it makes it harder to count the coins with your thumbnail.

The €.05 also has no milling, but is about 1½ times the diameter of the €.01 so is readily distinguishable from it. The 1, 2, and 5 cent coins are all copper-coloured.

The €.10 has milling at a pitch of about 3mm, so it actually feels lumpy as you run your fingertip around it.

The €.20 has, instead of milling, seven large (about 2mm across) notches equally spaced around its circular side. It recollects the design of the 20p coin but is larger, and has a notch at the bottom, whereas the 20p has a point at the top.

The €.50 has the same thick milling as the €.10, but it doesn't quite extend the whole way across the coin in the short direction, so it feels less knobbly. Also, the coin is larger. Still, mistaking a €.10 for a €.50 or vice-versa is the error I most frequently make. The 10, 20, and 50 cent coins are all bronze-coloured.

The €1 is quite distinctive. Divide the circumference into six equal segments: three of these have no milling, the other three have the usual fine-pitch milling we are familiar with on Sterling coins. The coin is also bimetallic: silver-coloured in the middle, bronze-coloured round the outside.

The €2 has the usual fine-pitch milling, like our £2 coin. It too is bimetallic, but the opposite way around: bronze-coloured in the middle, silver-coloured round the outside.

Some of you may remember that each Euro-using country mints its own coins, and can have its own design on the back of the coin. I suspect this is a ploy to keep coinage designers in work more than anything else. Interestingly, all of my Euro coins are French and Spanish, despite the fact that I haven't been in Spain since the Euro began, and I have been in Germany and the Netherlands. I think I spent all my Dutch change in France, and I don't think I spent any cash when I was in Germany, as it was a company junket, I mean, strategic conference.

So, as my collection of trivia has shown to be popular elsewhere, I have managed to concoct a post containing no important or useful information at all. I hope you enjoyed it, but not too much, as it might make me write more of them.