When deciding on a specific étude to pass out to a bari player, I had to check and see whether or not the horn had a specific key that's not yet standard on all baris...
ME: Let's see--your horn has a high F# key, right?
ME: Do you know how it works to make a high F#?
KID: You just push it down?
(I suppose he was technically correct here, but I was of course looking for a specific fingering combination...)