~~~~~~~
The civilian GPS timebase signal still has plenty of deliberate "jitter".
I recently put the coordinates for a "missing" survey stake into two identical GPS units. Then, I headed toward that point with the two GPS units -- and a hip pocket full of "pin flags"...
Every time one of the GPS units said I was on the coordinates, I set a flag there, and put the GPS down there to collect and average at least 1,000 readings.
Then, I checked the other unit, which invariably said the point was 50 feet or so "over yonder". Then, I went to that point, flagged it and set down GPS #2 to average 1000 readings.
Then, I went back to the other GPS -- whose "accurate" reading now said the point was 50 feet in yet another direction!.
After repeating the process several times, I had a rough circle of pin flags. So, I "eyeballed" the center, went there, kicked around in the leaves for a bit -- and, uncovered the "missing" survey stake!!.
~~~~~~~~~~~
Bottom line: civilian GPS might be accurate enough for bumbling around on roads -- but, you certainly can't drop a JDAM down an elevator shaft with it...