The heading for the Webber DGV Kit in the MSA catolouge says it is two barrel progressive. What does progressive mean in relation to the carburetors?

 

constant velosity carb I think. kind like SU

 

I have those webbers on my 72z.
They are two barrel and one is smaller than the other. The one barrel(smaller) is used mainly until the throttle is pushed more(almost half way floored) then the second barrel opens up. Therefore both barrels are not in use 24/7.
azguy
70 240Z
83 280ZXT