Letter = Time and elevation gain
A = Not strenuous (1-4 hrs, 600m elevation gain, day pack)
B= Moderately strenuous (2-6 hrs, 600-1200m elevation gain, day or overnight pack)
C = Strenuous (4-10 hrs, 1000-2000m elevation gain, day or overnight pack)
D = Very strenuous and multiple days
Number = Terrain
1 = Gentle slopes, mainly trails
2= Moderate slopes, travel off trail
3 = Off track in mountainous terrain, may involve steep forest and/or roped glacier travel
4 = Difficult mountainous terrain. Advanced backcountry and climbing experience needed.
5 = Leader protection, hardware required
6 = Direct aid climbing