WT_2007_06: TEST: SINN 757 UTC - Watchuseek, World's Most Visited ...

Advantages
+ Excellent cost-benefit ratio
+ Protected against magnetic fields
+ Scratch-resistant case
+ Aviation-influenced design
Disadvantages
– Simple strap
– Overly bulky case
178 WatchTime December 2007

Look,
With its extra-durable case
and resistance to harm,
Sinn’s 757 UTC boasts
super-heroic attributes. Now
this pilots’ chrono runs our
testing gauntlet.
BY JENS KOCH
PHOTOS BY NIK SCHÖLZEL
Up in
the
Sky…
Even if you don’t wear a cape and a
skintight leotard in public, and aren’t
charged with saving the world on a daily
basis, you’ll still find the tightly packed technological
cargo in the Sinn 757 UTC to be very
useful. A veritable Superman of a wristwatch,
this pilots’ chronograph is not only built to fly
through the air, it is nearly invulnerable:
scratch-resistant, protected against magnetic
fields, unfazed by low-pressure conditions and
resistant to cold and moisture. It is also
equipped with a second-time-zone display and
a bidirectional rotating aviators’ bezel. What
makes the case especially noteworthy is the
material from which it’s crafted: Tegiment
steel, which has a hardness of 1,200 Vickers.
This makes the case four times harder than a
case made of 316L stainless steel. Such extreme
hardness ensures that it can, like the
Man of Steel himself, emerge unscathed from
severe battering. The bezel, crown, and pushpieces
are also made from this uncommonly
hard material.
This watch’s gears are equipped to handle
extreme temperatures. Sinn applies its special
oil 66-228 to the gear train and pallet stones,
ensuring that the watch will continue to run
even if the temperature plunges to –49° or rises
to +176° Fahrenheit. The 757 UTC’s inner
case of soft ferrous metal protects the movement
against magnetic fields up to 8,000 amperes
per meter or 100 milliTesla. The same ferrous
material in the case is used for the dial, the
movement-holder ring, and the back of the
December 2007 WatchTime 179

TEST: SINN 757 UTC
The case is made of Tegiment steel, which has a hardness of
1,200 Vickers; that makes it four times harder than a typical
watch case made of 316L stainless steel.
case, providing effective protection against the
magnetic fields generated in a variety of everyday
situations. For example, fields as strong as
100 milliTesla can occur within three centimeters
of hairdryers, electric razors, or drills. A
magnetic field could momentarily slow an unprotected
balance, or worse, magnetize its balance
spring to long-lasting ill effect. Sinn uses a
special logo with a stylized magnet and field
lines, unostentatiously applied in glossy black
to the matte black dial, to symbolize its watches’
antimagnetic properties.
Making the Case
Another advantage is the absence of nickel in
the 757 UTC’s caseback. Just as magnetism
180 WatchTime December 2007
can be cruel to a watch movement, so too can
nickel be unkind to human skin. According to
the Nickel Institute, one in seven people is allergic
to nickel. That’s why Sinn crafts the back
of the 757 UTC’s case from nickel-free steel.
Even though the 316L alloy of stainless steel,
frequently used for the cases of watches, exudes
only 0.2 micrograms of nickel per square
centimeter per week — a value well below the
amount specified by the pertinent regulations
— even this is too much for some highly allergic
people.
The 757 UTC’s case is water-resistant to a
depth of 200 meters. While this is unusual for a
pilots’ watch, other types of watches are made
to achieve similar or greater degrees of waterresistance.
What’s unique about this one, how-
The impossible-to-lose rotating bezel, the push-pieces, the crown and the case are all made of
Tegiment steel. This watch can take punches.
DATA
SINN MODEL 757 UTC
Manufacturer: Sinn Spezialuhren GmbH & Co.
KG, D-60489 Frankfurt a. M., Germany
Reference number: 757 UTC
Functions: Hours, minutes, date, second time
zone, chronograph with counters for elapsed
seconds, 30 minutes, and 12 hours, rotating
bezel turns in both directions and is calibrated
with 60-minute markings
Movement: Self-winding Valjoux 7750;
28,800 vph, 25 jewels, Incabloc shock absorption,
Etachron fine adjustment with index, Glucydur
balance, Anachron balance spring,
48-hour power reserve; diameter = 30.4 mm,
height = 7.9 mm
Case: Stainless steel case, Tegiment-hardened
to 1,200 HV; impossible-to-lose, Tegiment-hardened
bezel with inset aluminum ring; sapphire
crystal is nonreflective on both surfaces; nickelfree,
fully threaded, screw-in back; screwed, Tegiment-hardened
crown; Tegiment-hardened
push-pieces; stay-dry technology; protected
against magnetic fields up to 80,000 A/m; protected
against low-pressure conditions; waterresistant
to 200 meters
Strap and clasp: Leather strap with stainless
steel pronged buckle
Rate results:
(Deviations in seconds per 24 hours)
(With chronograph switched off / on)
Dial up: 0 0
Dial down: +4 +5
Crown up: +2 +2
Crown down: +2 +4
Crown left: 0 +1
Crown right: +4 +4
Greatest deviation of rate: 4 5
Average deviation: +2 +2.7
Mean amplitude:
flat positions: 306° 297°
hanging positions: 283° 267°
Dimensions: Diameter = 43 mm;
height = 15.2 mm; weight = 124 g
Variations: With Tegiment-hardened steel
bracelet and secure folding clasp ($2,670)
Price: $2,370
ever, is the stay-dry technology Sinn developed
to keep the movement free from humidity. This
is important because moisture can be as damaging
to lubricant oils and movements as extreme
temperatures and magnetism.
A small amount of moisture ordinarily finds
it way past the insulating washers that protect
the interiors of watch cases. Sinn uses insulators
made from green Viton to combat the
problem. Manufactured from a combination

The movement, a Valjoux 7750, makes do without extra
embellishments, although the rotor boasts a fine sunburst
pattern and Sinn’s engraved insignia.
of fluorine and rubber, the material repels four
times more atmospheric moisture than conventional
nitrile insulators and is less sensitive
to heat and chemicals. Furthermore, Sinn uses
a desiccant capsule filled with copper sulfate
to bind whatever moisture might happen to
penetrate the interior of the case. A small viewing
window in the case’s flank shows whether
the copper sulfate is white (indicating it is still
absorbent) or whether it has turned dark blue
(indicating it has become saturated and the
capsule requires replacement).
Sinn also developed an impossible-to-lose
rotating bezel. Three screws on the bezel press
against a tension ring inside a groove in the
case. Because the bezel isn’t merely snap-fit, it
cannot pop off the case if you should happen
to knock it against a sharp corner. The bezel is
particularly useful in measuring intervals of less
than an hour with to-the-minute accuracy. To
do so, you set the luminous index on the bezel
in the desired position and read the number of
elapsed minutes by directly comparing the
minute hand with the easy-to-read scale printed
on the rotating ring. Originally developed
for airborne applications, this type of bezel
helps a pilot or navigator keep track of how
many minutes have elapsed since his airplane
passed one landmark and to calculate how
many minutes remain before flying over the
next. The optional countdown bezel, which
surprisingly isn’t mentioned in Sinn’s catalog,
makes this task even easier. The countdown
bezel lets you preset the interval remaining to
the next navigational point so you can begin
looking for the upcoming landmark when the
minute hand reaches the luminous marking.
A small but significant improvement has
been made in the sapphire crystal: rather than
being manufactured in Sinn’s usual blue or
purple hue, this one is simply colorless.
Crash Test
Viton insulators and an inner case made of soft ferrous metal protect the watch’s Valjoux 7750 against water and magnetism.
To check the durability of their watches, Sinn
gave a Model 756 — the model the 757 UTC
is based on — to the certifiers at the German
December 2007 WatchTime 181

For a little bit extra, you can equip the 757 UTC with a scratch-resistant, Tegiment steel bracelet
and folding clasp instead of this neatly crafted leather strap and pronged buckle.
car-testing company DEKRA, who strapped it
to the wrist of a crash test dummy. The impact
of the crash subjected the watch to 75
Gs of force, and had scarcely any effect on its
rate. Measurements conducted on the timing
machine before and after the smash-up varied
by less than one second per day. The
après-crash case showed no scratches thanks
to Tegiment hardening, a process that causes
carbon atoms to diffuse into the steel, thus
increasing the compressive stress in the alloy’s
surface.
The dark shade of the case’s bead-blasted
surface looks more like titanium than stainless
steel. Derived from the styling of Sinn’s
watches for navigational timekeepers aboard
aircraft, this wristwatch simply looks cool.
Anyone wearing one will look ready to climb
into the cockpit of a fighter jet. The dial’s legibility
is nothing short of phenomenal, even
under the most adverse conditions, but the
182 WatchTime December 2007
chronograph’s functions are not visible in the
dark. Only the hour hand and minute hand,
the number 12, the hour indices and the triangle
on the bezel are luminous. The second
time zone in 12-hour format has a yellow,
skeletonized hand, which clearly distinguishes
it from the ordinary hour hand. This display
is well suited for showing the time in UTC format,
the system most commonly used by pilots.
Also known as “Zulu time” in aviation
terminology, UTC stands for “coordinated
universal time.” To avoid cluttering and to
maximize the legibility of the dial, the watch’s
designers decided not to include a continuously
running seconds hand. They also left
out intermediate strokes for the elapsed seconds.
The date display is unobtrusive yet easily
visible at 4 o’clock, where the date appears
in white on a black disk without a frame
around it. The font for the numbers on the rotating
bezel is very similar to that used for the
Strapped to the wrist of a crash-test dummy in a test, the
watch was subjected to 7 Gs of force. The impact had
scarcely any effect on its rate.
numbers on the dial, creating a harmonious
overall appearance.
The leather strap isn’t quite on a par with
the refined, beautifully crafted case. The strap
and its stainless steel tang buckle are neatly
made, but rather simple. The former is machine-sewn
and semi-remborded, meaning
the upper leather is folded over the edges but
not over the filler as well. The prong on the
standard buckle isn’t milled, but merely bent
into shape. Sinn assumes this strap will be
subject to wear and tear, so the company of-
TEST RESULTS
SINN MODEL 757 UTC
Strap and clasp (max. 10 points): The simple
leather strap and the standard clasp are neatly
crafted. 7
Operation (5): The easily grasped bezel clicks
readily into place. It and the large screwed crown
are easy to operate. 5
Case (10): Thanks to scratch-resistant surfaces,
stay-dry technology, impossible-to-lose rotating
bezel, impeccable craftsmanship, and protection
against magnetism and low-pressure conditions,
Sinn’s case ranks among the elite. 9
Design (15): Although function clearly dominates
the foreground, or perhaps because of this,
the designers created a beautifully clear wristwatch
with typical Sinn design. 13
Legibility (5): What could be more easily readable
than large numerals, broad hands, and
bold indices? The time and the triangle on the
rotating bezel are distinctly legible at night. 5
Wearing comfort (10): The stiff strap and the
thick case detract somewhat from this watch’s
comfort on the wrist. 7
Movement (20): The Valjoux 7750 is a wellknown
and durable movement. Here, it has
been augmented to include a second time
zone. Sinn’s special oil helps it run accurately
throughout a broader range of temperatures.
And Sinn orders the caliber in “top” ETA quality
with a Glucydur balance. Embellishment is
given only to the rotor. 13
Rate results (10): Scarcely any deviation among
the several positions, slight decline in the amplitude
of the balance when the chronograph is
switched on, and small average deviation: this
movement performs with chronometer-worthy
accuracy. 9
Overall value (15): The cost-benefit ratio is
impressive. Most other manufacturers would
charge several times as much for a wristwatch
with similar attributes. 15
TOTAL: 83 points

Long-lasting
lubrication
Safety disk
Functional
plane
Pin
Button is guided
through the case
Groove
Flank protector
Serially
arranged
Viton
insulators
Return
spring
Sinn dispenses with the tube. The impact of
a blow is transferred to and absorbed by the
case.
fers a replacement for $80. An additional
$300 will get you a 757 UTC with a Tegimenthardened
stainless steel bracelet. This
bracelet offers greater longevity, although the
watch is more handsome with the leather
strap. The strap is quite stiff at first, but it
soon “learns” to fit comfortably around your
wrist. The case’s height is somewhat problematic.
If you’re not careful, it’s likely to snag.
Fortunately, the bezel and case are both
scratch-resistant.
On the other hand, the height is advantageous
because it makes the bezel easier to
grip. The chronograph’s push-pieces likewise
operate easily in response to only slight pressure.
The screwed crown, which sets the time,
is easy to operate. The date display has a rapidreset
mechanism. And the second time zone
display can be quickly advanced in hourly increments.
The ETA Valjoux 7750 chronograph movement
was given a second-time-zone display
without increasing the height of the base caliber.
The necessary parts were designed, developed,
and built by La Joux-Perret in La Chauxde-Fonds.
The movement makes do without
extra embellishments, although the rotor
boasts a fine sunburst pattern and is engraved
with Sinn’s insignia. Sinn opts for a caliber in
“top” ETA quality, which is technically identi-
Impossible-to-lose rotating bezel: screws press
the elastic ring (yellow) into the case.
cal to chronometer-worthy quality. This is evident
in the tapering spokes of the balance:
only Glucydur balances have such tailored
spokes, so their presence is a sure sign that
this caliber belongs to one of ETA’s top two
quality classes.
Knowing this, our expectations were high
for the rate performance, and this Sinn didn’t
disappoint. The daily deviations in all positions
ranged between 0 and +5 seconds,
which means that this timepiece keeps time
with chronometer-worthy accuracy. The chronograph
doesn’t sap too much energy, either:
the amplitude of the balance declines only
slightly when the stopwatch mechanism is
switched on.
Despite the watch’s many attributes, its
price is still in Sinn’s usual, reasonable range:
$2,370 is a very low price for such fine quality
and so many technical highlights. The 757 UTC
is the flagship in a small collection of Tegimenthardened
pilots’ watches with impossible-tolose
rotating bezels. The collection, which debuted
earlier this year, includes a 757 chronograph
version without a second time zone
($1,970), as well as Model 857, which lacks a
chronograph function but offers a second time
zone in 24-hour format ($1,580). Both of these
watches are endowed with the same super
powers as the 757 UTC. ■
December 2007 WatchTime 183