Diameter of the Magic Circle in Magick: Elemental Theory

Edit: This should be the Magick section. Had the number 93 stuck in my head
Recently, I went to measure the diameter of the magic circle in Magick : Elemental Theory. Grabbing a protractor, that was in centimeters, I found it to be 9.3 centimeters!
This got me wondering...
What is the best system of measurement to use when constructing "magickal items"? 
@Uni_Verse said
"What is the best system of measurement to use when constructing "magical items"?"
Somewhere in either Crowley's writings or the Golden Dawn papers (or maybe the Corpus Hermeticum...?) are some statements about the human body being the ultimate system of reference.
In the old days, the length of the King's foot was the definition of the "foot."
Aren't we aspiring to be Kings, here?
Steve
PS: Another idea could involve using some object that has special significance to you as a unit of measure. A favorite "found object," from nature, possibly? Or maybe something specifically Thelemic: like the "line drawn" on the manuscript of III:47 of the Book of the Law?
Whatever is chosen as the basic "unit," one can then take integer fractions or multiples that have some kind of Qabalistic significance...

As an exercise I measured the distance from the ground to my navel, which came out to be 41.5 inches. Round that up you get 42 inches or 3 1/2 feet.
Length of the center column 21 feet, base 17.5 feet, diameter of circle 60 feet.
42 : the world (also terrible name of God )
21 : Being
17 : "nuts" !