Noticed the wiki page of

https://en.wikipedia.org/wiki/Boundary_markers_of_the_original_District_of_Columbia

They got "Download coordinates as: KML"

Then open that with google earth.

The middle one is

Center of the square of the original District of Columbia

Source: Wikipedia article Boundary markers of the original District of Columbia

Looks like it's

38°53'35.15"N

77° 2'26.88"W

Now let's check the DC diamond left corner and right corner to see what their N's are.

West Cornerstone of the Original District of Columbia

38°53'35.68"N

77°10'20.28"W

The right side of the diamond

East Corner Boundary Marker of the Original District of Columbia

38°53'34.30"N

76°54'33.00"W

You'd think those N's would have to be all the same, right.