July-August - Air Defense Artillery School

A l-.lEclHOD OF E~lERGENCY FINDING
lOreany accurate survey data are available for base lines.
In any case a modified Crichlow rule such as the one
shown is recommended
batten'.
as a useful device to ha\'e in the
Th~ rule may be made any convenient size depending on
the range and accuracy desired. This particular one was
purposely drawn 14~ inches in diameter for mounting on
a standard circular ply-wood disk that can be found in
the vicinity of certain portable type army buildings. The
IO!! o scale is the same as that of the Crichlow, but the angular
scalesis in degrees and represents the sine rather than "one
O\'erthe sine." The angular scale is plotted with reference
tothe log scale, using a table of natural sines. This method
aroids the use of reciprocals or cosecants and seems to be
morepractical in this instance. The two arms can be made
of a strip of X-ray film if nothing better is available. The
center screw device must be manufactured or borrowed
from a standard rule. One of the anus is labelled R and the
other T.
To use the rule, a base line of three or four hundred
I'ards,or longer as desired, is laid out and measured to the
nearest yard. The Bl station should be in the vicinity of
thedirecting point; with the B2 station on the right or left
according to terrain conditions. The two base end stations
,hould be intervisible if possible to simplify the orientation.
Zero azimuth is down the base line from the right hand
station to the left hand station. If the two stations are not
inten'isible, datum points will have to be established. A
pair of phones connects the B2 reader with the operator of
the rule; and another pair, the Bl reader with an assistant
operator, who performs the subtraction, Bl minus B2
(angle T). The directions for the manipulation of the
arms, though simple, should be recorded on the face of the
rule. Tracking may be coordinated in the regular manner
using either a TI system or stop watch. A percentage range
corrector will also be required for conversion to mils and
for the application of corrections.
An improved version of the rule designed for more rapid
and accurate operation is suggested where manufacturing
facilities are available. Make up the log scale on a separate
disk capable of rotation about its center, and devise a way
for mechanically locking the arm T to the disk at any
desired point on the scale. The reading line of the ann
can then be fixed at any point so as to coincide with any
length of base line. The log scale would then rotate with
arm T, and by holding arm R on the value of B2, and setting
arm T on the value of the target angle (Bl_B2). The
range could be read immediately on the log scale under
arm R, and the possibility of error caused by slippage between
the two arms would be eliminated.
A treillendous, costly, long-enduring task in peace as
well as in war is still ahead of us.
But, as we face that continuing task we 11layknow
that the state of this Natio'n is good-the heart of this
Nation is sound-the spirit of this Nation is strong-
.the faith of this Nation is eternal.-FRANKLIN D.
ROOSEVELT.
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