I have racked my brain for the reason the Ancient builders chose 39.37 as a base unit at Giza and I think I have discovered the reason. I knew it had to do with distances in our solar system and especially Mercury and The Earth. Firstly Egypt was a Sun worshiping religion and I suspect that they would worship and take note of the day they were closest to their God and that would be January 4th of any given year. And since the evidence seems to be mounting that Giza is in fact an astronomical text book it would seem they also chose the average distance of Mercury from the sun in relationship to this closest distance of Earth to the sun as their base measurement.
so here is the solution:
Closest distance of Earth to The Sun God Ra = 147.09 million kilometers
Average or semi major axis of Mercury = 57.91 kilometers
147.09 / 57.91 = 2.5399 or reciprocal is .393705
I am sure Clive Ross' work on G3 in regards to Mercury and Mars is now as correct as he could get. So just how did the Ancient builders know that Mercury's average distance from their Sun God was .3937 of The Earth's closest approach to Ra ? ... Well at this point I am not quite sure and am open for suggestions.