Staad Pro - Critical moment calculation according to Eurocode 3

Hi everyone!

I am analysing a Channel section according to Eurocode 3 and I am finding it hard to understand how Staad calculates the critical Moment (Mcr)

The critical moment I get from the program is different from the one I get from "Annex F of DD ENV 1993-1-1"

Can you please explain what is the expression used?

Thanks a lot!