180 YEARS OF

duced in 1939. Unique to its type was the central pair of
hands that could be controlled by a push-piece. Pressing
the push-piece caused the horizontal clutch to open and
the hands to remain in position until the push-piece was
released, at which point they began to advance again immediately.
e reset function required pressing down the
push-piece fully. is type of mechanism required fewer
components, so Longines was able to omit the costly column
wheel. Moreover, its height of 5.9 to 6.1 mm was
also easier to work with. Even though the manufacture
used high-quality components such as a Glucydur screw
balance and a self-adjusting overcoil hairspring and
spared no expense in nishing, the price was still considerably
less than other conventional chronographs. But
sales did not achieve expected levels due to massive
export restrictions during World War II.
e extraordinary Siderograph was also introduced
in 1939. is watch represented a complex development
in the evolution of the Lindbergh Hour Angle watch used
to determine exact longitude in aircra navigation in
combination with a sextant. Its most striking feature was
the nely detailed dial design that permitted degrees and
minutes to be read in sidereal time. To accomplish this,
Longines’s watchmakers adapted the hand-wound
movement 37.9 to equal the duration of the average
sidereal day, which is three minutes and 56.555 seconds
shorter than an average solar day. e Siderograph was
not designed to tell standard, civilian time (measuring
exactly 86,400 seconds per day). e split-seconds jaws
and column wheel were mounted on the back of the
watch movement. A resetting device was essential in this
case. Pressing the pusher at 4 o’clock stopped the split
seconds. Pressing the pusher again allowed it to catch
up and synchronize with the continuously advancing
second hand.
Sidereal time model
“Siderograph” with
double rattrapante
and contacts for time
signals, from ca. 1940
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Steel model “Stop
Seconde” from the
1940s. Hand-wind
Cal. 12.68Z Stop,
diameter = 27 mm,
height = 6.1 mm,
central 60-minute
totalizer. Production
began in 1938/1939.
LONGINES SPECIAL WatchTime | 47