Choke is a performance, not a measurement. The measurements of the physical restrictions in the barrel vary with each bore and are designed to give the one range/pattern spread with which we are all familiar.
Choke is a measurement, but also a term which instigates confusion. No mater what choke, skeet or extra full if you are on the target with the correct size and load of pellet, it's a hit.
Try pattern testing for real and not with percentages etc and you will have a surprise or two.