Scooterotica

Hello, on the exploded view of the mikuni carb. it refers to the throttle valve affecting throttle from 0 to 3/8, needle jet affecting from 1/8 to 5/8 throttle opening and the jet needle affecting throttle from1/4 to 3/4. Can anyone explain what these refer to - throttle valve is the pilot, needle jet the clip on the needle and jet needle being the needle itself?

Thanks, Chig