Currency conversion challenge for author

Have you any idea what a challenge fluctuating exchange rates are for the author of mathematics text books? In Mathematics Explained for Primary Teachers I use currency conversion to illustrate 'direct proportion'. This is a really useful example of the concept, which can be shown as a straight line graph passing through the origin. In the 3rd edition, I had such a graph to illustrate conversion from euros to pounds. In 2006 you could exchange 29 euros for (about) £20, which was perfect for my purposes. Come to the point of writing the fourth edition and the exchange rate had changed drastically, with £1 down to about 1.10 euros at the start of 2010. What a nuisance! It looked as though I would have to draw a new graph. However, the US dollar came to my rescue! Conveniently, £29 now converts to about $20! So all I had to do was to change the labels on the axes (euros to pounds, pounds to dollars) and the corresponding words in the accompanying text. Brilliant!

But the currency exchange markets are still very unstable. Who knows what this will look like when the book comes out later in the summer? And in four or five years time?

So, as a rather unusual kind of 'currency speculator', I shall be checking the exchange rates regularly in the coming months (and years) in the hope that the dollar stays stable against the pound – and my example does not look too dated too soon!