On Mon, 10 Aug 2020 10:56:59 -0700, wrote:

Yeah, I didn't consider the monument moving. I live practically on top
of the South Whidbey Fault and there is motion associated with both
the fault and the whole region. The plate Whidbey is on is rotating
clockwise and just a few miles from me the island is moving a couple
millimeters per year.

Look for a "GPS Control Points" map on your county GIS web page or map
source. Here's mine from 1994:
https://gis.santacruzcounty.us/DPWScans/recordmaps/087M48.pdf
The notes under "Basis of Bearing" explains how the map works.
However, I barely understand the terminology and need to ask for help
before I can probably decode it. Anyway, you should have something
similar available. If you can find two or more such markers, you
should be able to orient your position plot to the map and adjust the
GPS locations.

Just to make things difficult, the above GPS Control Points map used
NAD83, while the GPS standard is WGS84. Fortunately, these are within
1 meter of each other in most of the USA, so I can ignore it for now
and use an online converter later:
https://geodesy.noaa.gov/cgi-bin/HTDP/htdp.prl?f1=4&f2=1


--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558