I want to make a point here.
Will you please draw a line through the blue line on the left going the length of New Hampshire Avenue at the same angle. (I make the angle 52.83. Jim Alison says different - see below). Then copy this and reflect it and place it on the right from the point of the apex. You will note that it goes right through the pink spot showing the location of the Capital Building.
On his website, bigbytes is also not so hot on the accuracy issue when it suits him, he writes:
By means of his map measurements he [Jim Alison] determines the angle of New Hampshire Avenue as 53.47 north of due east. Try putting a measuring device on his map image and see what you get for that.
Personally, I am going with Don Barone and Gary Osborn on this one, and suggest that the planners' intention was to depict the ~ 52 degree and 23+ degree angles inherent in the pyramid form, that is, that the triangle in the map was meant as a silhouette of the Great Pyramid's cross-section.
I said in my eariler post in similar words that my view is that in regard to Pensylvania Avenue that begins at 23.5 degrees to the White House, and from the White House alters to 19.5 degrees, the planner's intention was to depict the same 23.5 degree angle, but that perhaps they ran into a practical problem of some kind, perhaps with the location of the CB.