COAST ARTILLERY, JOURNAL - Air Defense Artillery

PROFESSIONAL NOTES 561
the spotting observer himself can make the conversion instantly and accurately
without the least interference with his most important duty of measurement of
the deviation. The spotting board operators are thereby left free to concentrate on
accurate application of the simple data coming over the line from the spotting
station.
The angular-linear deviation converter is simplya circular multiplyingsliderule
with specialnotation. It can be made of cardboard,thin metal, or any suitable-material
that may be available. It consists of two concentric logarithmic scales, the outer
FIG. Z.
fixed and the inner moveable. The outer, or range-deviation scale (a, Fig. 2)
extends through the entire circumferenceof the circle with notation fmm I to 1000.
The graduations of the moveable interior, or angular deviation scale (b, Fig. 2).
are identieaI with the exterior scale graduations from 1 to 60, but a special is
substituted for the ordinary notation. There are three alternative notations for
each graduation of the scale b. One series, marked "Left," starts with 3.05 and
runs to 6.00 with .05 intervals. The second, marked "Right," starts with 2.95 and
runs to 0.00 with .05 intervals. The third series is marked "Mils" and runs from
I to 60. An index (C, Fig. 2) is placed to the right of the 3.05-2.95graduation
hy the amount of the difference on the logarithmic scale between the logarithms
of 1 to .87. The moveable scale is pivoted at d, Fig. 2. The scale a represents