Bob; I see what you are saying. I will wait until I get the chips d more before asking more questions. Ronald Hi As mentioned multiple times in the archives. As you get into the single digit milliseconds, the human eye simply can’t keep up. A watch that is 1 ns off and one that is 1 ms off are both “good enough” if you are looking at it with a normal eyeball. >From a design standpoint 1 ms / day / week is *way* different that 1 ns over the same sort of period. Design constraints *do* make a big difference. It’s important in any project to get them sorted early. If you are spending $5K on a CSAC, tossing in another $100 on a GPS isn’t going to even get into the roundoff error. You *will* need the GPS gizmo to keep the CSAC calibrated. It is only a question of how often the beast gets used. Bob On 1/29/18, Ronald Held <ronaldheld@gmail.com> wrote: > >

Hi Questions are good, it’s how you figure things out. We’re talking about a “practical” timing device design. It’s not as crazy a topic as it might seem. Some basic math: You get to a million seconds at about 11.6 days. A millisecond error over that period is one ppb. If you are off 1 ppb at T=0 and stay there, you will be off by 1 ms. If you drift so you are off by 1 ppb at the end, you will be off by less than 1 ms. At some point, you do need “rough numbers” to work out what you are going to do. Holding a few microseconds (not milliseconds, we just jumped a factor of a thousand) on a GPS based wall clock / watch is quite practical, even with poor GPS access ( = crummy antenna). With a reasonable antenna 100’s of ns are very practical, even with a cheap GPS module. The practical question would be: What am I getting from the CSAC? One basic answer might be “holdover” at less than 1 us / day. Another basic answer might be autonomous operation in a location where GPS simply isn’t available. Lots to think about. Bob > On Jan 29, 2018, at 12:44 PM, Ronald Held <ronaldheld@gmail.com> wrote: > > Bob; > I see what you are saying. I will wait until I get the chips d more > before asking more questions. > Ronald > > Hi > > As mentioned multiple times in the archives. As you get into the single digit > milliseconds, the human eye simply can’t keep up. A watch that is 1 ns off > and one that is 1 ms off are both “good enough” if you are looking at it with a > normal eyeball. > > From a design standpoint 1 ms / day / week is *way* different that 1 ns over the > same sort of period. Design constraints *do* make a big difference. > It’s important > in any project to get them sorted early. > > If you are spending $5K on a CSAC, tossing in another $100 on a GPS isn’t > going to even get into the roundoff error. You *will* need the GPS gizmo to > keep the CSAC calibrated. It is only a question of how often the beast gets > used. > > Bob > > On 1/29/18, Ronald Held <ronaldheld@gmail.com> wrote: >> >> > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there.