Petrie makes the following statement in ‘Wisdom of the Egyptians’ (1940), p. 71:

“The result of this system was that the royal cubit was 28·28 digits, commonly reckoned as 28 digits, and on one cubit rod the digit value is exactly retained, and the last digit lengthened, to make up 1·28 with the fraction.”

Can someone please enlighten me as to which cubit rod it is that Petrie is referring? (I have done my googles without success. I can only find the rods with equal sized finger spacings).

A quality pic or a published diagram of these two differently sized fingers (and palms) would be greatly appreciated.