The problem with Mark Musgrave's report is that it is too generically stated, lot's of ambiguously rounding off of values throughout, which leaves too much room for error. Although when I saw the chart that showed what the averaged value of an AE RC unit total was for the Speed of Light, it did seem close enough to the Radian angle now utilized in trigonomic calculations, to do some more precise figure evaluation. None of the known Royal Cubit values I have studied over the years, proved to be as neatly nested as what I call the Fundamental RC unit of ratio 12/7 Imp.Ft. But at a reduced unit value of 57.375 unit/degrees minus all those extraneous trailing 0's, it did seem to be a bit too large to be of practical use. The standard definition of a decimal Radian being 180*/Pi = 57.296 degrees after rounding off the last digit. But that all depended on what value of Pi one was working with to make simplistic adjustment conversions to more precise values. This idea was known long ago in the case of certain Pi values such as the Babylonian usage of integer values 25/8 = 3.125 Pi, being converted to the more precise value still much used today of 22/7 = 3.142857 etc., otherwise known to some as seked 7/5.5, used in the construction of the GP. The conversion factor being the ratio 175/176 between the two Pi values. A Radian value in the case of the latter Pi unit is 180*/(22/7) = 57.2727 decimal degrees, which undershoots the current value by a tad, but is still a workable unit as well. But when I looked at what the conversion ratio between these two Radian values was, I was very surprised to see it was a very familiar figure I had been using for a long time in other studies of the Earth's dimensions formulated by using different AE RC units to calculate variations in the Earth's size between the Polar Meridian and Equatorial variance in Oblate size. In order to introduce this conversion ratio, I will have to do a quick review of my previous studies once again for those who haven't been following this line of research in a while.
The Polar Meridian Circ. of the Earth is 25,000 Mi. x (175/176) = 24,857.9545 Mi. (It should be noted that this is the same conversion ratio as those two ancient Pi values also.)
The Equatorial Cir. is 25,000 Mi. x (255/256) = 24,902.34375 Mi. These figures can be converted to two different AE RC units for Polar and Equatorial size as 8750^2 = 76,562,500 AE RC at 12/7 Imp/Ft.ratio for Polar Circ., and 76,500,000 AE RC units of 20.625 ins. for the Equatorial Circ.
The difference between these two dimensions of the Earth is the ratio (561/560) to convert Polar to Equatorial.
So when I go back and look at the aforesaid ratio between the Fundamental AE RC of Radian Speed of Light at 57.375 unit/degrees, and the secondary Pi Radian of 22/7 = 57.2727 unit/degrees, it is also (561/560).
I don't know what other metrologic researchers might have to say about this enormous coincidence, but to me it is just further evidence that not only was the Earth's dimensions known to a precise level, but also the Speed of Light as well.