Abrams SC-1, Technical Manual

Page: 16 / 39

MAINTENANCE MANUAL
SECTION
IV.
OPERATION
1.
CONVERTING
WATCH
TIME
TO
SUN
TIME (Apparent Time).
a.
General.
—
Because
the
operating
principle of
the sun
com
pass
is
based on
determining direction
from
the shadow cast
by the sun, the time
piece used
must
be set
and maintained
on
sun time. Sun
time, called apparent time,
is
based on
the move
ment
of
the
sun which
is
found
to be
irregular
throughout the
year while
watch time
is
based on a
standardized
system of
regular time adopted
by
the countries
of
the
world for
con
venience's
sake.
To
convert local watch time to local apparent
time
(local
sun time)
it
is
necessary to perform
a
series
of
time
changes and
to
fully
understand the terms applied
to them.
•
6.
Standard
Time.
(1)
A
system
of
time called
"standard time" has
been
adopted
by
nearly all nations
of
the
civilized
world. The
world
has
been
divided
into
24
imaginary
longitudinal
sections called
time
zones
(see
figure
6),
each zone
representing
one
hour
of
the
24
hour day.
Theoretically,
these zones
should
be
of the
same
size and
shape.
However,
referring
to figure
6
we
see
that due to
political division,
some zones
have very
irregular
boundaries and have adopted times which are not standard
for
the
zone
in
which they theoretically should lie.
(2)
The
system
of
standard time was developed
by
taking
Greenwich,
England
as the
prime meridian and establishing
24
different time meridians
around the world,
15 degrees
of
longitude apart,
so
that, standard times
in
zones
would
agree
with
Greenwich
in
minutes and
seconds but
differ in hours
by
whole numbers.
That is, when
it
is
12:20 A.M. in Greenwich,
it is
1
:20
A.M. in
a
city in
the next time
zone east.
All
the
clocks
iif
a
time
zone
are
set
to agree
with
the time
based on
the time
meridian in
the center
of
that
zone.
This
is
true
if
the people
within
the
zone
have not adopted a different time
for
economic reasons.
c.
Changing
from
Fait
to
Standard
Time.
(1)
It
happens
that in many
cases,
for
reasons
of
saving
daylight
hours, many countries or
zones
within
a
country have
adopted the standard time of
the
zone to
the east
of
them.
8