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English
Accuracy.
Mechanical watches measure
time accurately and reliably.
However, in circumstances where
optimum accuracy timekeeping
is required at all times, the
mechanical watch is not the best
instrument for the job. Time is
important to the wearer of a
mechanical watch, but accuracy
to the nearest second is not
something the wearer is likely to
lose sleep about.
The accuracy rate of a mechanical
watch depends on the type of
movement used, on the wearer’s
personal habits and on fluctuati-
ons in the ambient temperature.
Oris watches are checked and
set in the workshop, so daily rate
variation is within a tolerance
range of – 5 to + 20 seconds per
day. Chronometers are set and
tested to tighter tolerance ranges
than this (see Chapter on ‘Oris
Chronometers’).
If a watch is not keeping to time
within these limits, it can be set
by an approved retailer or at
the Oris service centre in your
country. During the guarantee
period, this service is free of
charge.
Notes.
Chronometer.
D
A Swiss watch can only be
designated as a chronometer if
its Swiss watch movement has
satisfied a test as per the
standards NIHS 95 -11/ISO 3159
and conducted by the independent
Swiss Observator y’s Contrôle
Officiel Suisse des Chronomètres
(COSC).
The chronometer test at the COSC
takes 15 days. All tests are
conducted at an ambient humidity
of 24 %. Every 24 hours, the
variance is measured, then the
movements wound and reset. On
the tenth day of this test, any
complications on the watch, such
as the chronograph, are switched
on to determine the movement’s
operating rate accuracy. The
movement rate is determined in
five different positions and at
three different temperatures, as
shown opposite.
If the movement passes the test,
it receives a certificate confirming
its rate accuracy and its status as
a chronometer. Every movement
is identified with an engraved
number and a COSC certification
number.
Day0123456789101112131415
Pos. 6 H 3 H 9 H F H C H 6 H
T °C 23 23 23 23 23 23 23 23 23 23 23 8 23 38 23 23
R(s/d) R1 R2 R3 R4 R5 R6 R7 R8 R9 R10* R11 R12 R13 R14 R15
*Any complications are activated.
Test criteria Ø (mov.) Ø (mov.)
All figures in seconds (s) per day (d) Abbrev. > 20 mm < 20 mm
Average daily rate
(in 5 different positions) Mmoy – 4 to + 6 – 5 to +8
Average rate variation
(average daily rate difference in 5 positions) Vmoy max. 2 max. 3.4
Largest rate variation
(difference between two rates in the same position) Vmax max. 5 max. 7
Flat-suspended difference
(between horizontal and vertical position) D – 6/+ 8 – 8/+ 10
Largest difference
(between average daily rate and rate in one of the 5 positions) P max. 10 max. 15
Thermal difference
(variation per °C of temperature difference) C ± 0.6 ± 0.7
Rate reproduction
(difference between average variation on day 15 and
average variation on the first two days of the test) R ± 5 ± 6
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