mechanical linkage for percussion firing is enabled. His right footrest is at one end of this linkage, and the firing pin sear in the breech block is at the other. By rocking his right foot forward, he fires the gun. Electrical firing is the primary firing method. When the Mount Captain commands, "Match pointers. Switch to Automatic.", he looks down at the dials on his Indicator-Regulator. The dials tell him the difference between the gun's present elevation and the ordered elevation electrically coming from the Fire Control System by synchro. He changes the elevation of the gun, by moving his hand wheels, until the dial difference is zero. His dials are now "matched", and he switches the elevation drive into Auto. This disengages his hand wheels, and gives elevation control to the Fire Control System. Then, he moves the Electrical Fire Select Switch to "AUTO", and reports back to the Mount Captain, "Elevation in auto." He may now look through his sight, and if the Sight Setter has matched the sight-setter dial pointers, he will see the target in the cross-hairs. When the Mount Captain commands, "Switch to Local", he switches the elevation drive and the Electrical Fire Select Switch to local. In local control, he controls the gun's elevation with his hand wheels to keep his sight's horizontal cross hair on the target. At the command of the Mount Captain, he fires the gun by squeezing the firing key on his right hand wheel. Trainer Controls the mount's train angle (bearing). He sits in the right front corner of the mount (see the far right man in the Mk21 open mount picture). In front of him, are his optical sight, hand wheels, and train drive controls. Between his knees is a large box called the Train Indicator Regulator. (pictured) This box controls the train power drive. On top of the box, is a window with a set of dials that indicate the train angle of the gun, and the automatic train orders electrically coming from the Fire Control System by synchro. When the Mount Captain commands, "Match pointers. Switch to Automatic.", he looks down at the dials on his Indicator-Regulator. The dials also tell him the difference between the gun's present train angle and the ordered train angle. He changes the bearing of the gun, by moving his hand wheels, until the dial difference is zero. His dials are