First computer with real-time clock?

David> Regarding a message that appeared on this thread with the David> approximate quote: David> of over a minute per dat David> [sorry I it the delete key too quickly on the message to post David> the EXACT text] David> 1 Day = 86400 seconds * 0.01% [100 ppm] = 8.64 SECONDS per David> day. Oops. David> Not good enough for long term time keeping but much better David> than the previous poster indicated. Yup. Right conclusion, wrong numbers. David> I was involved in the development of som Military systems David> [1979-1983] that used a tempe0rature stabilized crystal with David> 0.5ppm stability. To the best of my knowledge this was a David> "state of the art" implementation of automomous time keeping David> for 1979. 0.5 ppm for boxes that get carried around in military trucks and bounced around in the field -- that's quite good. For something that's sitting in a reasonably controlled environment, that's not so great; I think that 10^-8 would be considered state of the art for OXCOs (1970s or not). For autonomous timekeeping independent of technology, the state of the art was a second per year or so (that's 10^-8, roughly) around the early 1900s. First with pendulum clocks (Shortt clock), then around the 1940s or so crystal clocks came in that could match this. And not too long after that there came the rubidium (10^-10) and cesium (10^-14) clocks. Some of that would be found in military gear, I think (Rb at least, Cs somewhat less likely). Consider GPS satellites, which have either or both built-in. paul