[time-nuts] Time nut newbie

[Jim Lux]

On 4/30/13 4:18 PM, lists at lazygranch.com wrote:
> A bit OT, but back in the day there was what amounted to an X-prize for a real accurate chronometer for navigation.
>
> Make that way back in the day.
> http://en.m.wikipedia.org/wiki/John_Harrison

And he had a heck of a time collecting.  I suspect collecting an X-prize 
might be easier (assuming you've met the conditions).


The wikipedia article talks about the absolute error in the various 
clocks (5 seconds for transatlantic passage) but doesn't ever say how 
long that passage was.  I did find another reference that gave 28.5 
minutes of longitude over 5 months. If a degree of longitude is 4 
minutes of time, then that's an error of about 120 seconds out of 13 
million seconds, or 10ppm.  That *is* impressive for a mechanical device.

Another story (H5 clock in Kew gardens under supervision of George III) 
has 4.5 seconds error over 10 weeks, a bit less than 1 ppm.

He had previously built temperature compensated pendulum clocks which 
achieved 1 second/month, which is about 0.3 ppm.


The OP is shooting for about 30ppb (1 second/year).  Of course, he'll 
spend a bit less time and money than Harrison did...<grin>