Arms There are 4 different options for your Generation Chair arms:
No Arms Pretty self explanatory.
Fixed Arms 9.5" above the seat (10" if you opt for the thin seat foam) these arms do not adjust at all. You have 21.5" in between armrests. Armpads measure 9.6" long x 4.3" wide.
Height-Adjustable Arms 6.125" - 10.625" in range for placement above the seat (6.625" - 11.125" for thin seat foam) and 21.5" between the armrests. All you do is lift a lever on the outside of the armpad to adjust arm height.
High-Performance Arms These also offer the same height-adjustability as above as well as pivoting armpads that are width and depth-adjustable. They adjust 2" in width (1" per arm) 1.5" in depth and pivot 45 degrees. The inside distance between the armrest ranges from 17.5" - 19.5".
Which should you go for? It really depends on your needs. Most people opt for the high performance arms for several reasons. The features allow you to rest your shoulders and maintain an ergonomic posture no matter what height you or your desk is. It also allows you to quickly move them out of the way when exiting the chair.