Kellogg 3810 design manual

[ShilohReuel]

Good day all
I've been browsing through the MW Kellogg Design Manual 3810, and came across the concept of linear moment of inertia. I have attached the paragraph from the 3810 design manual.

If I look at the general equation for moment of inertia of a rectangular section, I = bd^3/12.
However, in this manual for Figure III, I = b^3/3. I'm trying to get around this concept with no luck. Can someone please explain this 'Linear Moment of Inertia', and how did the author get to I = b^3/3.

Your assistance in this regard will be highly appreciative,

 

[robyengIT]

because he consider the width of rectangule as 1.
If You write the normal formulas and You substitute the width with 1, You get these results

 

[denstan]

Govendes,
Equation given in Kellogg 3810 is basic engineering equation for I and can be found in any textbook and derived using fundamental principles.