This complete package of mouth reed calls effectively reproduces all the sounds of a herd of elk. The Sentry Plate Single has a Sound Plate that automatically positions it in your mouth at the right place and angle, making calling elk easier. The plate is set at 16 degrees, ideal for cow, calf talk and spike bull bugles. The Ivory Plate Single has a Sound Plate that positions it in your mouth at the right place and angle. The plate is set at 30 degrees for cow, calf talk and satellite bull bugles. The Imperial Plate Double has the Sound Plate, which is set at 30 degrees for cow, calf talk and satellite bull bugles. The Hyper Plate Double has 2 reeds with a Y-cut in the second reed, which is perfect for hyper, Estrus cow talk and herd bull bugles. The Sound Plate automatically positions the call in your mouth at the right place and angle.