Clock drift. Not strictly a Linux question.

[Tony Alfrey]

Roger Oberholtzer wrote:
> It's Friday. Time for a weekend-think-about-it question.
> 
> I think I am doing my maths correct. I am checking a PC's clock against a 
> high-end Trimble receiver (> $2000), using the pulse per second signal. 
> Unless I am doing something wrong, I seem to see a 0.02 % linear (over the 
> time I have looked) drift in the PC's clock (via gettimeofday()) compared to 
> the pulse from the GPS. 

Silly boy, this is clearly a general relativity problem.  The pulse 
you're getting from the GPS is from a geosynchronous satellite, at a 
radius of some 25,000 miles, whereas your box is in Sweden (I seem to 
remember?), where the Earth's crust is particularly thin and so you are 
close to the mantle.  Therefore, the gravitational field at the location 
of your box is considerably higher than at the geosynchronous satellite. 
  And from general relativity, we know that clocks run slower in higher 
gravitational fields.

This is also why Swedes age slower than the rest of us.



-- 
Tony Alfrey
tonyalfrey at earthlink.net
"I'd Rather Be Sailing"