or ... find information elsewhere:
An Explanation of Ratings and Grades
The Yosemite Decimal System
(even if i wanted to pay; i don't have $20 right now!)
my search for "class" produces this:
Attempting to define "4th class". Drew Brayshaw
my attempt to access that article produces this:
You must be a paid member to view Reference Article.($20 CDN/year)"
thanks.