[time-nuts] Discussion of precise time and frequency measurement

Jim Harman j99harman at gmail.com
Mon Nov 13 14:39:49 EST 2017

On Mon, Nov 13, 2017 at 12:32 PM, Gregory Beat <w9gb at icloud.com> wrote:

>  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?
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I think one nautical mile per second is a bit off:

86,400 sec/day
Earth's circumference at lat. 41 is about 16,200 nautical miles, so it's
about 16200/86400 or 0.187 mi/sec

There is an interesting book "Longitude by Wire" by Richard Stachurski that
describes efforts in the mid 19th century to improve the accuracy of
surveys and determine the precise position of North America relative to

This culminated in the use of pulses on telegraph lines to transfer
observatory time to remote stations. With this technique, very careful
measurements, and mathematical advances they were able reduce the longitude
uncertainty to less than 10 feet.


--Jim Harman

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