I have heard that for a period of time every day (anywhere from 15 minutes
up to an hour), the military completely scrambles the GPS system, and that
during this period, your GPS readings are off by a considerable amount.
And, this can happen any time of the day as it isn't a scheduled event. I
was also told that the military has GPS units that are significantly more
accurate than what the commercial units are. This information was given to
me by a fellow who took a class about how to use the GPS system in the
Alaska backcountry.

Any other Tweets hear of this quirk with the GPS?