Set your panel SCHEME width to the overall you wanted 7'-4"
Then set your division snap points to thirds and draw in the vertical frame members.
I agree, always let the program do the math.
Erika
Architect, Consultant
MacBook Pro Retina, 15-inch Yosemite 2.8 GHz Intel Core i7 16 GB 1600 MHz DDR3
Mac OSX 10.11.1
AC5-18
Onuma System
"Implementing Successful Building Information Modeling"