Original: They are designed to be used in order: A scrub plane, which removes large amounts of wood quickly, is typically around  in length, but narrower than a smoothing plane, and has an iron with a curved cutting edge.
Simplified: They are designed to be used in order: A scrub plane, which removes large amounts of wood quickly, is typically around 9 inches (230 mm) in length, but narrower than a smoothing plane.