Abrams SC-1, Technical Manual

Page: 26 / 39

MAINTENANCE MANUAL
when traveling east and subtracted when
traveling
west.
One
degree
of longitude is approximately
49
miles at
45
degrees
latitude and approximately
69
miles at the equator.
(2) To Determine an Unknown
Azimuth.
(a)
If
it is
desired
to
know
in
what direction
a
vehicle is
headed, the
solar plate is adjusted
to the proper date line on
the
date bar.
(b)
Rotate
the
shadow bar
to
coincide
with
the
intersection
of
the
time and latitude
lines which represent
your latitude
and
time (according
to
local apparent
time).
(c) Turn the date bar, solar plate, and shadow bar as one
unit until
the shadow cast by
the center gnomon rod falls
on
the
shadow bar.
(d) The
arrowhead
on the
date bar is pointing
to the degree
mark
on the
protractor
of
the
sun
compass,
which
is
the
azi
muth of the course
on
which
the
vehicle is
headed.
(3)
Maintaining
the
Course
6j/
the
Use
of Foresights.
(a)
In
order
to keep on
an accurate course of travel, fore
sights
on
distant objects located
between the
vehicle and
the
final destination should
be
taken as often
as
possible. The
vehicle should
be
stopped, the
compass
leveled,
and
a
sight
made
on
a
distant object by
aligning
the
object and
the
sighting rod
screwed into
the
gimbal arm, with
the
gnomon rod. This
distant
object
is
some
object in
the
direct line
of
travel when
the
vehicle has
been
oriented
on
its
course
as
explained in
paragraph
3
—
b.,
section
IV.
The
vehicle
is
steered in
as
di
rect
a
line
as
possible towards the
selected
distant object until
it is reached
;
then
a
new reference point is
selected
and
this
procedure continued
until
the destination
is
reached.
The
vehicle must
be
stopped
and
the
compass leveled
for
an accurate
reading. Readings may
be
made
when
the
vehicle
is in
motion
by
taking
them
at the instant when the compass
is judged
to be
level.
Deviations from
a
straight
course,
compulsory or other
wise, may
be
corrected
for
en
route
by
changing the course of
the vehicle
until
the
amount of deviation has
been overcome.
(b)
In
featureless
terrain
the
vehicle is
steered on a
direct
line of travel towards the final destination
by
constantly keep
ing
the
shadow of
the
gnomon rod in coincidence with
the
18