Also, if you always point your gps pole the same direction, it tends to eliminate pole bubble error.
If your pole bubble is off 0.02' @ 2 meters height, and you observe ctrl station number 1, facing north, then ctrl station no. 2 facing south, you just threw 0.04' horizontal error between these 2 pnts.
Shoot points twice with the same point number, rotating the rod 180° in between. That should tend to average out error due to pole plumbing. If the variance between the two is as much as 0.02' it's time to adjust the bubble or increase the time on station. I generally get about 0.01' "splits" with a pair of 15 second occupations taken within a minute of each other.
I take two consecutive 10 or 15 second shots, rotating 180 between. I consider that one observation. If there is no other check I return under a different constellation and repeat. That has worked for 20 years so I'm going to call it good procedure...
Just like friends don't let friends scale without truncating, friends should not let friends set controls with poles and bi-pods. If your going to set a gun up on it you might as well set it with a tri-pod.
Thanks for all the replies! I need to do some research and figure everything out.
Oops! I didn't word that real good.