Origin of Baselength and height of GP (no replies)

I have been operating on the view that Petrie created the theory of a baselength of 440 Royal Cubits and height of 280 Royal Cubits. However, a re read of his survey indicates in ch 21 that the theory was in existence prior to his survey and his survey confirms the theory. Refer to

[www.ronaldbirdsall.com]

Given Petrie doesn’t provide references for the origin of these theories, does anyone here know?