737 Classic.
Before Take off, FLT selected gives minus 200' of departure field. This reduces noise, helps stops fumes ingressing into cabin and helps lessen the pressure bump after take off. CRZ alt selction is to ensure a max diff is acheived when at final crz alt. On landing the press controller drives the pressurisation to minus 200' from the alt selected in the landing alt window. This is for the same reasons as above. The sby window is only used when sby mode is selcted. You just have to change the selections in the window in line with the above instead of the auto controller sensing the aircraft flt path and doing it for you.
One point though. Minus 200' equtes to 1.25 psi (i think...), which is I think the max pressure allowed under JAR ops (again, "I think") when an aircraft is on the ground. This is because all aircraft doors must be capable of being OPENED wilst on the ground and pressurised. This is to protect against flt deck incapacitation etc..... And I have forgot to go to gnd after landing
The first I knew about it was a breif rush of air rearwards when our number one muscled open the door.
I stand to be shot down in flames and corrected though........
Mr L.