michael.cook@sfr.fr said: >>> prior to my senior project most geodetic surveyors used a Wooden boxed, >>> marine chronometer, to get sub second UT1 time, or back then, GMT >> How did you get the data out of the wooden box? > I have a couple of marine chronometers that have electrical contacts > closing once a second. This signal is relayed by wires to terminals on the > outside of the box. That gets you seconds if you count them. How do you get sub seconds? Just count time since the PPS using a normal crystal and it will be good enough? -- These are my opinions. I hate spam.

> Le 13 nov. 2017 à 12:12, Hal Murray <hmurray@megapathdsl.net> a écrit : > > > michael.cook@sfr.fr said: >>>> prior to my senior project most geodetic surveyors used a Wooden boxed, >>>> marine chronometer, to get sub second UT1 time, or back then, GMT > >>> How did you get the data out of the wooden box? > >> I have a couple of marine chronometers that have electrical contacts >> closing once a second. This signal is relayed by wires to terminals on the >> outside of the box. > > That gets you seconds if you count them. How do you get sub seconds? Just > count time since the PPS using a normal crystal and it will be good enough? In a sense.. When I was in the merchant navy in the 60s there were no crystal watches, so when taking sights we « transferred time » to a good 1/5sec stepping deck watch previously synchronized to the chronometer which of course was kept in the shelter of the Bridge. As this was done just prior to sights the offset would be known to less than or equal to that increment. Marine chronometers may not be particularly accurate, but they can be extremely stable at about +/- 0.2sec or better per day variation. The daily drift being known from the clocks last rating, getting accurate offset timing from GMT was possible. The clocks themselves were re-rated every year. I’m in France and I don’t think that any borders in Europe were defined by astronomical observation, but in the US I believe that at least some of the state borders were thus fixed. As a second’s error in time will be about a nautical mile in US latitudes, I wonder if anyone has measured with GPS, how good the original surveys were.? > > > -- > These are my opinions. I hate spam. > > > > _______________________________________________ > 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. "The power of accurate observation is commonly called cynicism by those who have not got it. » George Bernard Shaw

The TV series "How the States Got Their Shapes" mentions boundary errors occasionally. There were some magnificent errors that took years to resolve. In most cases today, the boundary is what it is and the fact that it's a few inches or feet in error is usually ignored. Many boundaries are a function of watercourses that change over time; the Mississippi is famous for doing that such that there's actually a part of Illinois (I think) on the west side of the Mississippi because the river changed its course. Jeremy On Mon, Nov 13, 2017 at 5:10 AM Mike Cook <michael.cook@sfr.fr> wrote: > > > Le 13 nov. 2017 à 12:12, Hal Murray <hmurray@megapathdsl.net> a écrit : > > > > > > michael.cook@sfr.fr said: > >>>> prior to my senior project most geodetic surveyors used a Wooden > boxed, > >>>> marine chronometer, to get sub second UT1 time, or back then, GMT > > > >>> How did you get the data out of the wooden box? > > > >> I have a couple of marine chronometers that have electrical contacts > >> closing once a second. This signal is relayed by wires to terminals on > the > >> outside of the box. > > > > That gets you seconds if you count them. How do you get sub seconds? > Just > > count time since the PPS using a normal crystal and it will be good > enough? > > In a sense.. When I was in the merchant navy in the 60s there were no > crystal watches, so when taking sights we « transferred time » to a good > 1/5sec stepping deck watch previously synchronized to the chronometer which > of course was kept in the shelter of the Bridge. As this was done just > prior to sights the offset would be known to less than or equal to that > increment. Marine chronometers may not be particularly accurate, but they > can be extremely stable at about +/- 0.2sec or better per day variation. > The daily drift being known from the clocks last rating, getting accurate > offset timing from GMT was possible. The clocks themselves were re-rated > every year. I’m in France and I don’t think that any borders in Europe were > defined by astronomical observation, but in the US I believe that at least > some of the state borders were thus fixed. As a second’s error in time will > be about a nautical mile in US latitudes, I wonder if anyone has measured > with GPS, how good the original > surveys were.? > > > > > > > > -- > > These are my opinions. I hate spam. > > > > > > > > _______________________________________________ > > 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. > > "The power of accurate observation is commonly called cynicism by those > who have not got it. » > George Bernard Shaw > > _______________________________________________ > 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. > -- Sent from my iPad 4.