(_a_) Fire-control and power section: 1. Observing detachment— _a._ M′ detail. _b._ M″ detail. _c._ M‴ detail. 2. Plotting detachment— _a._ Plotting board detail. _b._ Communication detail. 3. Power detachment— _a._ Casemate detail. _b._ Searchlight detail. (_b_) Planting and loading section: 1. Planting detachment— _a._ Planter detail. _b._ Small-boat details. 2. Loading detachment— _a._ Loading room detail. _b._ Explosive detail. _c._ Cable detail. (_c_) Gun and ammunition section: _a._ Gun details. _b._ Projectile detail. _c._ Powder detail. (_d_) Reserve section: As required. In each company assigned to the mine defense, a permanent manning table will be made out and always kept up to date. A copy of this manning table will be posted in the mine commander’s station. In addition, a copy of such portion of this table as pertains to any particular station will be posted therein. =Plotting board.=—The plotting board differs from that used for guns in that it requires no gun arm and corresponding attachments. Furthermore, since the distance at which mines are planted will in general be small, the board, without any change in size, may be used with a much larger scale, say, 150 yards or even 100 yards to the inch, and the arms graduated accordingly. The stations are manned during the planting of mines and the location of distribution boxes, as well as during operations. [Illustration: FIG. 15.—PREDICTION RULER.] For planting buoys signals may be made from the primary, from the secondary, or from both, as conditions warrant. Observations are taken on each mine as planted, the data are recorded, and the position of each mine is plotted. During operations vessels may be tracked by the vertical or by the horizontal method of position finding. If by the former, either the command “Fire” may be given when the vessel is on the cross wires of the instrument set at the range and azimuth of a mine, or the time from any point to the instant of passing over a mine may be found by means of the prediction ruler (see below) and the command “Fire” be given at the proper instant, as indicated by the stop watch. For the horizontal base system the latter method must be used. =Prediction ruler= (fig. 15).—This is a 10-inch white celluloid slide rule with a beveled edge. The slide is graduated in “Yards in 15 seconds,” and on the left and right of the runway, respectively, are a “Fire at time” and a “Yards to mine” scales. The beveled edge is graduated from the center outward in both directions with “0” in the center of the scale and “500” at either end. Each 50 and 100 has its value engraved on the scale.