THE COAST ARTILLERY JOURNAL - Air Defense Artillery

210 THE COAST ARTILLERY JOURNAL
II. METHOD OF PLOTTING
1. Introductory. From the foregoing explanation it is seen that the same
data are obtained from both camera and visual spotting units; i. e., the devia-
tions of the individual bursts and the azimuths of the target at the first and the
last bursts, from each of the two terrestrial stations. From other sources the
following data were obtained and used for the final plot of hits on the danger
volume.
Altitude: obtained from the height finder.
Angu lar height: obtained from the height finder or B. C. instrument.
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2. Horizontal Projection oj Target's Course. a. Having the azimuths of
the target taken at the same instant from two accurately located stations, the
horizontal projection of the target at that instant can be readily plotted.
b. For this purpose an impro\'ised board with brass arms, one pivoted at
each station, was used (Figure 4). The scale of this board was 1 inch equal
to 100 yards. By use of the azimuth scales drawn on the board (4 al1d 5) the
arms were laid at the azimuths of the target at the first burst and the intersection
plotted. This, then, is the plot of the position of the target on the horizontal
plane at the beginning of the firing on this course. Similarly, the position was
plotted for the end of the course, using the azimuths of the target at the last
burst. Assuming the target to fly in a straight line, a line joining these two