e6b

Does anyone know what that weird black circular attachment is on the ASA E6-B is? For the life of me, I can't see any use for it.

So far I've gotten an iPad Air 2 with a couple good cases (folio keyboard for notes and school work and an OtterBox for when I'm on the go), a David Clark H10-30 Headset (ancient but it's tried and true), a Noral Student Pilot Flight Bag to hold my headset, fuel tester, iPad, flashlight, med...