If you find a very old IWC wristwatch, chances are that it has a Cal. 64 movement or its successor, the Cal. 64T. Until 1915, the Calibre 64  was  the primary movement used by International Watch Company in its wristwatches.

The Cal. 64 actually was designed as a very small pocket watch movement, used in ladies’ pendant watches. Some reports date it to 1892 and others state that it was introduced in 1893. It was a "Savonette" (or "hunter") style pocket watch movement, which means that the seconds subdial would be a 6 o'clock with the crown at 3. 

There also was a corresponding Lepine-styled movement, the Cal. 63. A Lepine movement normally would show small seconds at 6 o'clock, with the crown at 12. When used as a wristwatch the crown would be a 3 o'clock, which then  would place the seconds subdial at 9.  As such, most  wristwatch examples that used  Lepine pocket watch movements, such as the Cal. 63, omit the seconds hand entirely. The Calibre 63 seldom was used by IWC in wristwatches, but the Cal. 64 was quite commonly used.. There are varying reports when it was first used by IWC in a wristwatch. The most recent reports claim that IWC produced its first wristwatch in 1898.

The Cal. 64 movement had a size typical of movements made today. It usually  was 12  ligne  (26.5 mm) in diameter and had a height of 4.1 mm. It had a typical pocket watch oscillating frequency of 2.5 Hertz (18,000 halfbeats per hour) and had a Breguet overcoil balance spring. 15 or 16 jewel versions were made. It enjoyed a long production life, from 1893 to 1917. A total of 41,440 were produced, but not all were for wristwatches.

The Cal. 64 was set using a pusher, which sometimes is called “pin set”.  Unlike modern watches, the crown does not extend to set the time. Instead, a small pusher at 4 o’clock (shown at left below the crown) is depressed, which disengages the winding mechanism and allows the crown to be used to move the hands. I have seen two types of pusher mechanisms used: the more common one  is depressed, usually by using a fingernail, but a few examples had a small flange that is pulled outwards. The  below image of a gold "half-hunter" styled Cal. 64 model shows the pusher that is pulled outwards to allow the hands to be set via the crown.

This setting mechanism can be somewhat awkward and the Cal. 64 was succeeded by the Cal. 64T. The movement was essentially identical except that it dispensed with the pusher and had crown setting. It was IWC's first movement used in wristwatches that had hand-setting via the crown. In addition, at least from visual inspection there was a change in three chatons, bushings that fit around jewels on the movement. In the Cal. 64, three of the chatons were screwed in place, while the Cal. 64T used one screwed chaton and two that were pressed in place.

There also are varying reports on the production dates for the Cal. 64T. Most reports state that was produced from 1917 until 1932, with a total of 10,800 pieces. However, a more recent report dates the movement from 1906 to 1931, with a total production of 12,030 examples. During this period, IWC introduced other small movements, so not all IWC wristwatches from the 1920s contain this movement.

Most examples said “International Watch Company Schaffhausen” in script on their dials. However, the above early "half-hunter" model says "IWC" in an oval on its rare black dial. I noticed one very early example, ca. 1910, that appeared authentic but had a plain dial: it was difficult to tell if it had a generic replacement or some dials were unsigned. In addition, a large number of these watches was exported to the English market. These apparently were cased by Stauffer & Co., IWC’s British agent at the time, and have different inside markings. Sometimes, the movements are marked “S & Co” and the inside casebacks say “Peerless”. Perhaps with a token of grace for their age, most collectors consider these watches “authentic” IWCs.

The Cal. 64 and Cal. 64T watches often can be found today in surprisingly good condition, although the silver does tarnish and will need cleaning.  Because they are relatively small, and neither shock nor water resistant, they do not enjoy as much popularity as some other vintage watches. While prices vary widely, I often see them in silver for around $1,000 and even in gold seldom for much more than $2,000 and frequently less. For the serious IWC watch collector, they can be historically important additions to a collection.  

Special thanks to James Dowling for the images of the half-hunter gold Cal. 64 wristwatch and movement.