A watch described as adjusted to positions has had its accuracy tested in a set number of different orientations. This matters because gravity acts on the movement differently depending on how the watch is held. Adjustment evens out the timing differences between those positions, so the watch keeps better time.
Which positions are used?
The positions chosen reflect the ones a watch is most often in while being worn. On a wristwatch, the first two are flat: dial up and dial down. The upright positions follow: crown down, crown up and crown left. Most present-day movements are adjusted in five positions, so crown right is usually left out. COSC, the official Swiss chronometer testing body, tests movements in the same five positions. Position does the most harm in the upright positions. Extra friction and a changed balance rate are worst when the balance spring stands upright.
What about railroad watches?
From around 1908, most American railroads required the watches used in their service to be adjusted in five positions. Not every railroad set this rule, but most did. Pocket watches adjusted in six positions were top-grade movements. They were usually made for railroad service. Adjusted watches of any kind usually cost more. The factory work took extra time and skill.
Not to be confused with
Positional adjustment is not the same as isochronism adjustment, which keeps the rate steady as the mainspring runs down. Nor is it temperature adjustment. On older pocket watches, a movement stamped only ‘Adjusted’ had usually been adjusted for temperature, not necessarily for positions. Take care with large totals too. A movement marked with eight or nine adjustments counts temperature and isochronism as well. It has not been adjusted in eight or nine positions.
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