You are part of a design team for a GPS system for mountaineers. During user interviews, you notice that most users tend to describe mountain climb difficulty as follows: F Facile (Easy); PD Peu Difficile (A little difficult); AD Assez Difficile (Fairly difficult); D Difficle (Difficult); TD Tres Difficile (Very difficult); ED Extremement Difficult (Extremely difficult). What classification system is being used?