I am wrong about Aubrey hole circumference. I accept Thom's value , Aubrey Burl also gave 285 feet as diameter.
816 is an interesting number and I have found it in cube roots.
However I am going to stick with 0.825 as the basis of the system.
0.825 x 16 = 13.2ins
0.825 x 25 = 20.625 Royal cubit ins
0.825 x 24 = 19.8 natural cubit 1 and 1/2 feet
9.9 ins Welsh foot a Great Span 3/4 of 13.2
Origin the Great Pyramid Kings Chamber dimensions length 412.5 inches or 20 Royal cubits 20.625 inches.
I agree we are all working on the same thing but coming from different directions.
you were damn right to stick with 20.625