The table top is covered with a local map covered with clear plastic divided into square kilometer grids. The metal item is a radial deflection fan used to plot the line from our guns to the target (moving the guns from right to left or left to right). The slide rule device calculates the elevation of the gun barrel and the amount of powder needed to reach the target (distance). The fuse type and any time settings depend on the reason for shooting; explosion on impact, delayed explosion after impact or explode in a set number of seconds after the round exits the gun.
The target location is sent by an observer to FDC for conversion to gun settings; but the line of the observer to the target may not be the same as the gun/target line so adjustments must be made to compensate for that. Our first round was unlikely to hit the bullseye, so the observer called a measure of our miss and FDC recalculated gun settings. The difference of our lines to the target distorts his observation relative to our shooting line. Read the full story. https://vietnamsoldier.com/accurate-artillery-fire-2/