The best feature of the Aimpoint PRO is the tension-locking mount system that fits any mil-spec picatinny rail.  After the sight is set in place on the rail, you simply turn the big, knurled knob until the torque setting clicks over three times to return the sight to zero.  I marked my rail with a pencil to make sure the sight went back in the same groove each time and it kept throwing rounds into the same group at 100 yards, no matter how many times it was dismounted and remounted.