How to read carb calibration chart?

if you haven't read this yet, at least glance through it.
Carburetor Fundamentals (Session 222) from the Master Technician's Service Conference

or you can watch the filmstrip
http://www.imperialclub.com/Repair/Lit/Films/222/index.html

Then you'll have a better idea of what changing sprigs or jets and other adjustments do.