Several methods are used to lay mortars parallel. The most rapid, but the least accurate, method is by using a compass. In this method the section leader stands approximately 6 feet behind the mortar and sights through the compass at a given direction. The section leader then directs the gunner to move the lay of the barrel left or right until the barrel and the sight wire of the compass are lined up. At this time the gunner

Figure 14-14.-Arm-and-hand signals used in placing out aiming post.

rechecks to see that all level vials are centered. When the center of the barrel and the sight of the compass are in line and all bubbles level, the gun is laid. The section leader then directs the gunner to refer the sight and put out their aiming posts. "Refernng the sight" means making a deflection change on the sight without moving the mortar. To refer the sight, you turn the deflection knob until the given deflection is set on the sight. When using the M64/M64A1 sight, you can place the aiming posts where they can best be observed because the deflection scale can be slipped to read the desired deflection. The sight (M64/M64Al) is initially referred to a O-nil reading, and the aiming posts are set on that deflection.