Abrams SC-1, Technical Manual

Page: 25 / 39

OPERATION
(b)
Loosen the clamping nut underneath the sun compass
and
turn
the
date bar
until
the arrow-head
terminating
the
direction line points to the degree
mark
on the
protractor
which represents the azimuth
of
the
course
to be
followed.
This
azimuth
is
determined
from
a map,
providing it
has
some
direction line
on
it
such
as
a
north
arrow
or projec
tion line.
This
is accomplished by
laying
a
protractor
on the
map
so
that
its
center point coincides
with your position and
the edge
is parallel
to a
true north and south
line
on the
map.
The destination point
is
marked
on
the map and
a
line
drawn
from
it
to
your
position.
The
clockwise angle formed
between
true north and the line
drawn
to
the destination
point from
your position is the azimuth
of
the desired course.
NOTE
:
The operator must
be
sure
that
the
azimuth
is
read
from
true
north.
(c)
Slide
the
solar plate along the date bar
until
the
straight
outside edge coincides
with
the date line
on
the date bar which
represents today's date. Both
sides of the date
bar
are the
same so
that
it
does not matter which
edge
is
used.
Clamp
the date bar and solar plate
in
position
by
turning
up on the
clamping nut.
(d) The
shadow bar
is
rotated
until it
coincides
with
the
intersection of the proper time and
latitude
lines.
The latitude
will
be
taken
from
the
map or instruments.
The
time
is
taken
from
the timepiece which
is
maintained
on
local apparent time.
(e)
The
compass
is
leveled
by
referring
to the level
vial
and
clamped. Then the vehicle
is
turned
until
the shadow cast by
the
center gnomon rod
falls
on the shadow bar.
The
vehicle
is
now headed on
its
course and the arrow-head
on
the date
bar points
to
true north.
(f
)
As
the vehicle
proceeds
along the course, the shadow bar
should
be
reset to
a
new time at regular
intervals
of
15
min
utes
—
the time being taken
from
the timepiece maintained
on
local apparent time.
If
the course lies nearly
east
or west, on long
fast jour
neys,
the longitude
will
change enough to require
a
correction
to
the local apparent time maintained
by
the timepiece.
(4
minutes correction
for
each degree
of
longitude)
to
be
added
IT