Figure 1-2. Indirect fire plotting board M17.

Figure 1-2. Indirect fire plotting board M17.

1 centimeter each. The first division, to the right

of the index line is equally divided into 10 spaces

of 1 millimeter each. The nine graduation lines

in the first division and all figures in the middle

scale are red.

( e ) The grid pattern (7) is inclosed

within an 8.000-inch circle. A series of l-inch

v e r t i c a l and horizontal squares and parts of

squares are located within the circle parallel

to the index and O. P. (observation post) lines

(2). Each complete l-inch square is divided into

Figure 1-1. Indirect fire plotting board M17 W/E.

100 equal squares. Twenty-eight incomplete 1-

inch squares, bordering on the circle, contain

of the base is graduated into 20 equal spaces.

varying amounts of smaller squares and parts of

The central graduation line of the scale is di-

squares. There are 78 equally spaced vertical

rectly above the centrally located index mark

and horizontal lines and 80 equal vertical and

(4). Ten equal divisions of the scale are located

horizontal squares along the index and O.P. lines.

to each side of the index mark. The vernier scale

All marking is red.

marking is red.

(f) The index line, passing through the

(d) At the bottom of the base (6) is a

center of the grid pattern, has an arrow touch-

triple map scale (5) graduated in meters with

ing the top inside diameter of the circle. The ar-

its legend and representative ratios of 1:50,000,

row points to the O (zero) index mark. A thin

1:25,000, and 1:5,000. These representative ra-

line, from the point of the arrow, intersects the

tios refer respectively to the top, middle, and

index mark and extends to, and becomes the cen-

lower scales. These scales are used to transfer

terline of, the vernier scale. This thin line is the

data to or from a map or firing chart which has

point on the plotting board base at which all

one of these scales. The triple map scale is 1

deflections are read. The index line is graduated

decimeter long and is divided into 10 divisions of

1-2