To parlay off of the other topic about DSC vs 3 whistle vs Dual...

What state do you work in, and which system(s) are allowed for varsity matches?

I guess I'm allowed to reply to my own post...

The Wisconsin Interscholastic Athletic Association adaptions to Natl Federation rules has the following entry:

Rule 5-1-1 Schools must use a single referee and two WIAA licensed assistan referees for all varsity duals.

So the DSC system reigns supreme here, most of the time

But the "varsity duals" language is interesting, because 4 teams can play 2 full length games in a quadrangular in one day...but the adaption means the schools can get away with having only 2 refs work those games.

Go figure.

Maryland - dual, all games, regular season and playoff.
Delaware - northern mostly dual, occasional diagonal
Delaware - southern mostly diagonal
Delaware - tournament diagonal (southern politics)
Pennsylvania - mostly dual, some triple, tournament triple
(no PA games lately, but think it's the same)

OhioHSAA:
regular season: one whistle, two whistle, or three
whistle

playoffs: Sectionals: two whistel
Districts, Regionals, and Final Four:
one whistle

MichiganHSAA:
regular season: one whistle, two whistle, or three
whistle

playoffs: three whistle

Nevada
Mostly DSC, but some games duals in regular season due to travel concerns at the smaller out-of-town schools.
Playoffs: DSC

Neither the High School Athletic Association nor any of the college conferences have officially decreed anything, leaving it up to the assigning secretaries to decide. I have not seen any assigning secretaries using three whistles. During the season they assign DSC or Dual; during post season - DSC.