Hamilton Khaki X-Wind Limited Edition
Hamilton Reference H77796535
45mm case diameter
14.85mm case thickness
Numbered Limited Edition (NLE) of 1,918 pieces
316L stainless steel construction
Sapphire crystal with anti-reflective (AR) coating
100m water resistance
22mm leather strap with steel rivets
Full tang stainless steel buckle
Hamilton Caliber H-21-Si Swiss Made automatic chronograph
Valjoux 7750 base or tractor
Hours, minuts, seconds, chronograph, day, date, drift angle
First ever ETA supplied movement with silicon (Si) hairspring
28,800 VPH (4Hz)
~60 hours power reserve
COSC certified chronometer
Hamilton H-21-Si Movement
The Hamilton H-21-Si movement is a fantastic option for this new version of the Khaki X-Wind Limited Edition. The H-21 uses the now infamous Valjoux 7750 automatic chronograph. Since Hamilton and ETA/Valjoux are both owned by the Swatch Group, it makes it much easier for Hamilton to get modifications done and done in-house. In the case of the H-21 (notice without the “Si” designation) has had the following reported modifications made to it:
- The entire kinematic chain has been refined, from the barrel to the escapement (note that a a kinematic chain is an assembly of rigid bodies connected by joints to provide a constrained or desired motion).
- The escapement regulator has been suppressed and this results in the facilitating if optimal reliability and precision.
- The main spring has been improved to increase the typical power reserve to 60 hours.
In the case of the H-21-Si, the movement has been further modified and, hence, the use of the “Si” designation. It refers to silicon and this is what the hairspring has been made from. One of the main outside factors that effect the accuracy of watch movements is magnetism. In the case of using silicon, the effects of magnetism on the hairspring are all but nullified. Of additional note, this is the first 7750 that is supplied by ETA that uses a silicon hairspring. Please note that this is not to say that that other brands (such as the German brand Damasko) have not done this themselves.
If you’d like to learn more about hairsprings in general and their overall importance in a watch movement, we would very much recommend watching the following video. It was put together by our friends at TheWatches.tv and does an excellent job in breaking everything down. While this is done in conjunction with the watch brand Bovet and not Hamilton, the information is good and generally carries across all brands.
The following short pormotional video is from Hamilton and covers both the H-21 and the H-31 movement. Note that the H-31 movement is based off of the Valjoux 7753 movement.
COSC Certified Chronometer
The Hamilton Khaki X-Wind Limited Edition is a COSC certified chronometer. Or, more correctly stated, the Hamilton H-21-Si is a COSC certified chronometer movement. Please note that this is NOT a chronograph. COSC stands for “Contrôle Officiel Suisse des Chronomètres” (Official Swiss Chronometer Testing Institute) and is a non-profit organization responsible for testing movements for accuracy and issuing the COSC certification. It is difficult to get full testing reports (the COSC no longer provides that information). But, generally, approximately 3% or so of all Swiss made timepieces receive the coveted certification.
The testing that a timepiece goes through to receive COSC certification is defined as follows:
Each uncased movement is individually tested for fifteen days, in five positions, at three different temperatures. The movements are fitted with a seconds hand and the automatic winding mechanisms are disengaged for the tests. Measurements are made daily with the aid of cameras. Based on these measurements, seven eliminatory criteria are calculated, each of which must be met (e.g., for movements of a diameter over 20 mm, the requirements, indicated in seconds/day, are noted in the table below). There is no ISO standard for quartz timepieces, but there is development in this field. ISO 10553:2003 specifies the procedure for evaluating the accuracy of quartz watches, individually and by lot, and the relationship between the accuracy tested and the accuracy classification given by the manufacturer.
The requirements of the COSC testing are defined as follows:
Average daily rate: -4/+6 seconds per day
This is the average rate over the first ten testing days
Mean variation in rates: 2 seconds
This figure shows if a watch tends to run fast or slow; a good quality watch will be consistent, whether it is fast, slow or correct
Greatest variation in rates: 5 seconds
This is the largest difference between any two days’ readings in a single position
Difference between rates in H & V positions: -6/+8 seconds
This is calculated by subtracting the average of the rates in the vertical (V) position (first and second days) from the average of the rates in the horizontal(H) position (ninth and tenth days)
Largest variation in rates: 10 seconds
This is the largest difference between the mean daily rate (see test number 1) and any individual rate during the first 10 days of positional testing
Thermal variation: ±0.6 seconds
The temperature error of the movement, expressed in seconds/degree
Rate resumption: ±5 seconds
This number is obtained by subtracting the average mean daily rate of the first two days of testing from the mean daily rate of the last test day
If you are unfamiliar with the COSC certification process or you’d just like to really go down the rabbit hole and learn much more about it, we recommend that you watch the following video. This is a video put together by our friends at Long Island Watch as a part of their “Watch and Learn” series. As is the case with all of the videos from the folks at Long Island Watch, they have done an outstanding job at putting this together. It is very much recommended to all!
If you prefer an additional (and shorter) video, our friends at TheWatches.tv also have a very good video that covers the COSC process. It, too, is highly recommended.
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