I know you're kidding, but check this out:

1 nanosecond is 1/1000000000 of a second, or 1.0 x 10^-9.

2 nanoseconds per day, cumulative error, 2.0E-9 * 365, is 7.3E-7.

Still doesn't sound like much? Light moves at 186,282 miles per second. In 7.37 x 10^-7 seconds, light moves 0.136 miles. Or 718 feet. Going from 11 to 8 nanoseconds improves positional accuracy a noticable amount.

Now I have never tried to substantiate this, but I've read that the typical eye blink is in the neighborhood of 40 milliseconds. Well . . . you asked. Let's see . . . one thousand one. . . Nope. One thou . . . Nope. One t . . . Nope. On . . . Nope. It's dang fast, that's for sure.

Only if your travelling near the speed of light <img src="/images/graemlins/smirk.gif" alt="" />

If you are stationary or moving relatively slowly (less than say 700 mph), the propogational delay shouldn't be much of a factor. My GPS doesn't update fast enough to be accurate if I am moving much more than 100 mph anyways, certainly at the highest resolution, where by the time it updates I am already several hundred feet beyond the marker and off the screen already.

Hmm, that sounds about right. Fractionally, I think the range for most eye blinks was between 1/20 and 1 60 of a second (50 milliseconds to 15 milliseconds).

Groo...
The time as recorded by the sattelites is periodically updated from the ground. So those errors never have a chance to accumulate. The ground stations have enough room for a really good atomic clock.

True. It's a contrived example. But people easily forget just how fast light travels. 1 nanosecond is just about 1 foot.

I figured the on board clocks received updates from the ground... I'm guessing the ephemeris is updated from the ground too. But the onboard clock accuracy improvement is still important. I wonder if the improved accuracy allows for either fewer updates, or better accuracy if ground based updates are... interrupted... for some reason. <img src="/images/graemlins/frown.gif" alt="" />