MIL-DTL-48559 Mount, Telescope And Quadrant - M172A1This specification covers the Mount, Telescope and Quadrant: M172A1 which supports the Fire Control Quadrant: M18A1 for use on the M777 and M198 series of howitzers and gives elevation compensation to correct for cant when the mount is leveled by a cross level movement. The mount also supports and aligns the mounting bracket for the Elbow Telescope: M138A1.