seven segment display history

On 28 Feb 2008 at 15:26, Jules Richardson wrote: 7-segment displays go back to the 60's at least--I seem to recall seeing a prototype 60's EL display using the technique. The RCA Numitron was about 1970, but it was by no means the first. I strongly doubt that 7 segment displays were used anywhere in the Apollo program for a very good reason--their failure mode. If a Nixie is bad, it doesn't light at all. If a single segment fails on a 7-segment display, the result can be an ambiguous reading with no indication of failure. For example, if the top segment fails, there's no way to distinguish between a 4 and a 9 in most displays. I think that the Apollo technology was neither incandescent 7-segment nor Nixie gas tube. I suspect, rather, standard projection displays, where a strip of film in the form of a loop is placed in front of a light source. They were modular and very easy to replace from the front of a panel. See, for example, the following photo from the Apollo 11 mission: http://www.hq.nasa.gov/office/pao/History/alsj/a11/ap11-S69- 39815HR.jpg (warning: it's big (558K). You can clearly make out the numeric displays (and the half-filled ashtrays) on the ops consoles. BTW, there are many very good photos at http://www.apolloarchive.com/apollo_gallery.html Cheers, Chuck