While messing around with some measurements the other day it dawned on me that pretty much every scope I've ever used [*] that has a bandwidth limit setting has a min setting at 20MHz. What I am wondering is, why 20MHz? It seems like more than a coincidence that every vendor & model would pick 20MHz. I am sure there are scopes with other min settings in existence but this definitely seems like the most common choice. * For me this means scopes built in 1990 & onward.