Create field output with max function

[n3l3]

Hi,

I am trying to see the envelope of a field output.
For that purpose I am trying to "create a field output" (I know how to do it for example for sum , divide... but i dont know how to create an envelope of the selected frames, since I get no function max or min in the "create field output" dialogue)

any idea?
thanks all
n3l3