Dave:

Go to Plate 13 and view his drawing of the chamber's four walls; it was too complicated to express in written format...a picture is worth a thousand.

You will notice that the slope and direction for each wall is equal for all layers; therefore the total height of the walls, at any given point, would be the same. Petrie states the variance with respect to the base of the “structure”; it's not a variance with respect to the chamber itself. He had to maintain uniformity in his measuring system, his start location was the north base and, as a true surveyor, all measures must be maintained with respect to this point.

You are correct…it is confusing when you see the numbers; it would be ideal if the measures had been prepared similar to the coffer readings. Guess we can’t have everything.

Best.
Clive