What does "graduated" mean?

Graduated: (Zoöl.) Tapered; -- said of a bird's tail when the outer feathers are shortest, and the others successively longer. Graduated tube, bottle, cap, or glass, a vessel, usually of glass, having horizontal marks upon its sides, with figures, to indicate the amount of the contents at the several levels. -- Graduated spring (Railroads), a combination of metallic and rubber springs.