Hermione Wrote:
-------------------------------------------------------
> After
> some
> searching around, I eventually found a
> reference leading to
> pgs
> 100-102 here: but I couldn't find any
> specific reference in that text to "Stride of Ra"
> and where it might have come from.
>
> Other searches have also proven fruitless.


The sources for the 'Strides of Re' are every royal Pyramid in Egypt, since these Stride-measures were not written on some transitory papyrus, but written in stone, in massive and immovable terms.
The reason for the ~34.1 feet height of the perimeter wall of the Djoser, and for the six Stride-high elevation of the Djoser Pyramid: built to the measure of the average Stride in (2670 BC) the first year of its construction.
The Red Pyramid was designed to 21 average Strides in base-length and to 10 Strides high in its (2587 BC) foundation year.
The base-length of the Khufu to 22 Strides in (2541 BC) the last year of its construction, that of the Khafre to 20.5 Strides in (2519 BC) the mid-year of its construction schedule, and the Menkaure to 10 average Strides in (2487 BC) its first year of construction in N – S dimension, and to 9.5 specific Strides in E – W dimension. Just in case the Giza architects' design plan was not understood in the future by some: G3-b and G3-c were structured as step-Pyramids to the base-lengths of 3 average Stride-lengths during their 2476 – 2472 BC era of construction, while the geometric G3-a Pyramid was built to the lengths of 4 specific Strides. To confirm, just in the unlikely case some in the future still didn't cotton on to the bases of Heliopolitan design: they structured the length of the KIng's Chamber to one average Stride during its construction era – and the lower base of the Bent Pyramid to 18.15 average Strides in length, the upper base-length to 11.85 Strides long: for a total of 30 average Strides / 600 cubits in (2592 BC) the mid-year of its construction schedule. Just in case...

The length of the Royal Cubit was indeed standardized in 2482 BC at 20.683": to a twentieth part of the Tropic's rate of travel in that year – in the year of the 64-day advance to the position of the Civil calendar, necessitated because of the continuing acceleration to the ground-speed of the latitude of the Tropic of Cancer (a more-modern misnomer, which has nothing to do with the stellar background of the Sun at the summer solstice during the pre- or early dynastic era).
Every Pyramid in Egypt, from the Userkhaf to the Ahmose, was built to the measures of this standardized average and/or specific Stride of Re.

You will find that the "stade of Eratosthenes" equates to 300 Royal Cubits: the 1,500,000 cubit ( / 5000 stade ) latitudinal distance between the central latitude of Alexandria and the location of the Sun Well of Syene on Elephantine Island, a Solar Well built long before the Ptolemaic era.
You will not find much else, other than the evidence written in stone, for the lengths of Re's Strides.

It has already been pointed out (reference / source) that the average length of the forearm in AE times measured 17.72". Not that facts appear to make much difference to opinions.