-Let this be the last post on this issue-
Your logic is impeccable but in practice it doesn't work because the floors are arbitrarily numbered.
The first 20 floors are actually more equal to 14 floors of 13'4" each, like most of the other floors.
I am not exactly sure of the math (Here is where Zen would step in and fill us all in) but trust me, 72 is the Octagon floor.
No, his logic was NOT impeccable. Don't make that assumption especially when it comes to this kind of issue. This really has nothing to do with floor height or building plans; it all boils down to the math:
Today I did a little mathematical exercise and was able to prove that the "octagon" is indeed on the 72nd floor. It took me some time to come up with, but in the end I figured out the height of the tower at which this "octagon" is found, which was 878 feet, and just about on the 72nd floor. To actually get the 878 figure, I used some pretty difficult triangle ratio methods and eventually mashed out this formula:
o=the height at which the octagon is found (the variable)
h=height of any one of 1WTC's triangular facades=1,183 feet
a=half of the base of any of the four larger triangle facades=100 feet
b=half of the base of any of the four smaller triangle facades=70.7107 feet
height of base=185 feet
Proving this formula would be impossible on this forum given that it is largely a geometrical proof and requires multiple diagrams to be drawn. The most important thing to know is that the facade triangles don't all have the same area (4 are larger, 4 are smaller) and therefore the octagon is a little higher up than just at the midpoint of the facade triangle height.
Also, does anyone know who first came up with the 72nd floor as the "octagon floor" that everyone keeps mentioning?