An envelope is a resultant (set of forces) in which one of the force values is a maximum or minimum for an item (such as a cross section) under consideration. All of the force values within a single envelope occur simultaneously.

Audit envelopes are created by the following process:

• for each rule set, 6 envelopes are added to a list (Max M, Min M, Max V, Min V, Max P, Min P)
• duplicates are removed (if Max M and Max V are identical, one of them will be removed)
• torsion conversion is performed (this can modify the torsion values, it can also create additional envelopes)

The result is a list of envelopes (possibly just one, but also possibly up to 12).