Seven segment display history

One thing I've always been really curious about is who invented the seven segment display. Not a particular implementation of it, but the graphic design concept that seven bars are all you need to display the digits 0 - 9. I'd always assumed it was something that originated from the creation of electronic calculators. The first Friden EC-130 for example, uses seven segment patterns on a CRT (machines prior to that used Nixie tubes). Well, leave it to Don Knuth to dig up a much older reference. While browsing his web pages, I noticed a reference to patent 974,943 by F.W. Wood, issued in 1910(!). It describes an electro-mechanical "Illuminated Announcement and Display Signal" with a segmented display. Wood actually uses eight segments (so his "4" has a slanted top), but other than that, it's exactly the same design as the digits today's cheap watches and calculators. Patent (you may need to register first): http://www.freepatentsonline.com/0974943.pdf Cheers, jp