[ntp:questions] National time standard differences

Terje Mathisen "terje.mathisen at tmsw.no" at ntp.org
Tue Feb 9 20:50:13 UTC 2010

Richard B. Gilbert wrote:
> David J Taylor wrote:
>> world, and that folks had to invoke relativistic corrections. Were
>> these better than microseconds as well?
> Please excuse me if I leave relativistic corrections to the late
> Professor Einstein! It's not something I've ever needed to know!

Oh, but you do!

Or at least your GPS does: The sat clocks vary in speed since the orbits 
are not perfect circles: This means that they run slightly slower than 
average when in a low orbit part, and slightly faster during the higher 
parts, so that the average is correct.

One of the corrections terms a regular GPS uses is a clock correction 
based on the orbit eccentricity and current altitude.

This also means that a GPS is the only piece of hardware most people 
will ever own that needs to consider Einstein.

- <Terje.Mathisen at tmsw.no>
"almost all programming can be viewed as an exercise in caching"

More information about the questions mailing list