Are u calculating too????
I too didnt got the question exactly, as there exist a curve on SUB & hence the ceiling height isnt constant (so blogger need to be much specific about the point of difference)!!
Kindly factor all skews, to arrive constant average!!
Mine is that, if u have any better option, kindly help blogger!!
PS:...
more... I am not in train, so cant measure each n every part, so offering equal options!!