While browsing the computer displays at the Science and Technology Museum I spotted something familiar. It was a Hewlett Packard calculator; the same model as the one on my desk. It seems that my favourite calculator is actually two years older than I am. After a bit of digging, I discovered that this calculator (which I bought for $5 at a garage sale) is not only historic, but is also a collector's item. They regularly sell on eBay for over $100.