Column Interaction Diagrams dont use f'c , why?

Sorry if this questions is basic. Working a problem on the 6 minute solutions I attempted to solve it by using the Column Interaction Diagrams from SP-17(14) (ACI Volume 3 Design Aids). I was nowhere near the possible answers and could not find my mistake. Finally I looked at the solution provided and realized it used the Column Interaction Diagrams from the Structural Engineering Reference Manual, except these interaction diagrams do not use f'c in the denominator for either term of their respective axis. Can  someone explain why? 

Don't remember the previous ones but the Eighth edition of Structural Engineering Reference Manual uses f'c = 4 ksi as shown in the header of the diagram.

Not familiar with the SP-17(14) but answer should come out the same or close though...

Andy Lin said:

Don't remember the previous ones but the Eighth edition of Structural Engineering Reference Manual uses f'c = 4 ksi as shown in the header of the diagram.

Not familiar with the SP-17(14) but answer should come out the same or close though...

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Hi Andy, Nice to see you here. I visit your site often. Yes you are correct, it is very close. I was thrown off by the missing f'c, but it work out close enough. Thank you for the reply! 

Hemi79 said:

Hi Andy, Nice to see you here. I visit your site often. Yes you are correct, it is very close. I was thrown off by the missing f'c, but it work out close enough. Thank you for the reply! 

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Nice -- glad to be of help!