What are the differences between Stillman & Birn sketchbooks?

Stillman & Birn Alpha Softcover Sketchbook 8x10

Review: Stillman & Birn's New Nova Series Toned Paper

Stillman & Birn Alpha Sketchbook Review

Review: Stillman & Birn Gamma Series Softcover 3.5 x 5.5 inch @StillmanAndBirn #Sketchbook #GammaSeries

Stillman & Birn Nova Sketchbook - Softcover - 5.5 x 8.5 - Beige

Why Do I Use Stillman & Birn Sketchbooks?

Softcover Stillman & Birn Sketchbooks: Initial Thoughts - Liz Steel : Liz Steel

Why Do I Use Stillman & Birn Sketchbooks?

Stillman & Birn Beta Series Softcover Premium Sketchbook - Artist & Craftsman Supply

Stillman & Birn Delta Series 5.5 x 8.5 Hardbound Sketchbook

Sketchbook System, Stillman & Birn