In the barrel ( BMUON) and rear ( RMUON) muon systems the magnetic field of the iron YOKE is used to perform a momentum measurement. Each chamber consists of two layers of limited streamer tubes with wires and perpendicular readout strips mounted on the inside and outside of the iron YOKE. For the barrel detector, the wires are in the beam direction, for the rear detector in the direction. The hit position resolution is better than . The barrel and rear muon detector can be used to measure the momentum of prompt muons but also cosmic muons.