This article is from the Token Ring FAQ, by James Messer James@NetworkUptime.com with numerous contributions by others.
The adjusted ring length of a token ring network is the sum of all
cable lengths between wiring closets, minus the shortest cable
between wiring closets. The ARL is used to determine the total
length of the ring, and the maximum lobe distances (see section [4.8]).
This calculation determines the ring length if part of the ring is
removed for troubleshooting. When a cable is removed from a Ring
In/Ring Out port, the loop-back creates a much larger ring than
normal. The ARL calculation defines the largest ring size that can
occur, based on the shortest cable between wiring closets.