[ntp:questions] National time standard differences
"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"
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