Complication guide
Ligne and movement size: how the complication works
The ligne is the traditional unit watchmakers use to state a movement's diameter; converting it to millimetres is the first step in matching a donor.
Watch movements are traditionally sized in lignes, a Swiss unit written with a prime mark, where one ligne is about 2.2558 millimetres. A movement described as 11 1/2 ligne, like the ETA 2824-2, is therefore about 25.6 millimetres across, and that figure is what a case is bored to accept.
Converting the ligne to millimetres is where any donor search begins, but it fixes only the diameter. A true drop-in has to match on height, on where the winding stem enters, on the hand-hole sizes and on the calendar layout as well, which is what the fitment tool checks caliber by caliber.
Related complications and calibers
ChronographA chronograph is a watch with a built-in stopwatch, started, stopped a
Automatic windingAn automatic, or self-winding, movement winds its own mainspring from
Date and day-dateA date complication shows the calendar date through an aperture; a day
GMT and second time zoneA GMT watch shows a second time zone on an extra hand that circles the
ETA 2824-2caliber and drop-in group
ETA 2892-A2caliber and drop-in group
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