Question re Dorf stair clearances

[susan]

Dorf says to use measure for a 6'-6" wide corridor (ctr line to ctr line) to make sure you end up with a minimum 6' clearance from wall to wall.
But when he suggests using a 10x20 stair in most cases....are we to assume that these measurements are ctr line to ctr line? Or should we be measuring 10'-4" x 20'-4"?
Thanks

[Coach]

All spaces are measured to centerlines by the computer. For stairs, just make sure the area meets the program; however, also make sure that the min dimension is 8' CLEAR.