What is every duty of a Field Captain in a high school marching band?

This is in a band with a Drum Major, Assistant Drum Major, and Field Captain. I was told I'd be conducting anytime they need me backfield, and I'd be in charge of setting drill as a student. I don't really understand if I'll have the power to call the band to attention, help with fundamentals or anything like that. Can somebody maybe help explain further duties?|||It's best to ask your director - that way there is no confusion and no stepping on toes.