The Egyptian Royal Cubit appears to have been produced by dividing the Nippur Cubit by a rounded off version of sqrt 2. They rounded off 1,414213562 to 1.4. 20.413386/1.4=14.58099. That is the Egyptian "construction Remen". The RC is then derived from the remen by making a square with sides of 1 construction remen, the diagonal is then 1 RC of 20.62063381". So the Nippur Cubit was the original diagonal of a square whose sides could be called a "Nippur Remen". But the Egyptians got their remen from that square by a purely mathematical means by rounding off sqrt2 to an even 1.4. That brings the number 7 into it, if you scale the 1.4 up 10 times to 14, 7x2. This made the units produced "Royal".
Edited by GS1, 23 September 2012 - 09:03 PM.