I'm newbie in OpenERP developpement, and i want to add some fields to opprotunity form view.

1) I want to add Picklist field for Stage and make probability field ReadOnly. Probalility should depends on stage change.

2) I want to add new field of type float (coefficient), ReadOnly and it depends on opportunity's probalility on the timing of creation:

                        If probability <50% then coefficient == 1  
                        Else if probability >50% then coefficient == 0.1
                        Else coefficient == 0.5

Once the coefficient is calculated for the first time, it should not be changed.