Mitch,

SWMM output text gives the same description when using F3 or F4 lines.
Seems they are doing the exact same job? As I mentioned, even SWMM
manual is describing the two lines F3 and F4 exactly the same. You will
find F3 lines describing NKLASS 11 and F4 lines describing NKLASS 21 are
exactly typical. They need the same inputs and produce the same text
description as seen in the attachments? Again, I am using SWMM 4.4h at
this moment if it makes a difference.

Thanks
Hazem