Inflation-busting web gadget

If you’ve ever wanted to calculate the value of something in real terms, removing the effect of the inflation rate over time, it can be a real pain. So I finally got round to building a little web app which does precisely that – for prices as far back as 1750. Why? Because I fancied the challenge.
You can use it in two ways. One is the ‘Time Machine’, taking the price of an item for a given year, and calculating the equivalent price for a different year, based solely on the effect of inflation. So for example, I remember CDs costing 12 quid each in the mid-80s. If they had kept pace with inflation, they should now be costing nearly double that.
To calculate the ‘real terms’ movement in an item’s price, removing the effects of inflation, there’s also the ‘Up or down?’ tool. Type in a ‘before’ year and price, and an ‘after’ year and price, and the tool tells you the percentage rise or fall over that period.
It’s all relatively simple, I suppose, but I’ve used it as an opportunity to experiment with some exciting new technologies: namely Scriptaculous, Prototype and a bit of Ajax. It uses some basic PHP to do the various data lookups behind the scenes, rather than any database. I’m especially pleased with the slider controls to let you select a year (with conventional text boxes if you don’t fancy that). The design is a bit old-school, but it wasn’t meant to be a design challenge. 🙂
Update: It’s entirely coincidental that this should be on the same day that ONS launches its own interactive personal inflation calculator, with the aim of ‘(allowing) individuals to see how differences in spending patterns affect inflation rates.’ It’s all done in SVG, but I’m having real trouble using it in Firefox. Surely plain old HTML (souped up with ajax goodness), with a dash of Flash if necessary, would have been better?
There are a few documents explaining all about it available from here but be warned, you’re going to face usability issues, with or without documentation. (Simon’s first law of usability: if it needs instructions, it’s too complicated. A two-page PDF is a pretty spectacular breach of this law.)