A sub-dial is a smaller dial set inside a watch’s main dial. It shows information beyond the basic time of day, such as seconds, minutes, hours, a second time zone or the date. It is most often used for small seconds or for counting a chronograph’s minutes.
What can a sub-dial show?
A sub-dial can show seconds, minutes or hours. It can also show a second time zone, the date or other calendar information, or how much power reserve is left. Some sub-dials are simply printed on the main dial. Others are set into a recess in it, so the smaller dial sits lower than the surface around it.
How do chronograph sub-dials work?
On a chronograph, the sub-dials are the counters, also called totalisers. They record how long the stopwatch has been running. The minute register counts the elapsed minutes. Some chronographs add a second sub-dial that counts the hours. The hands on these registers are driven by the chronograph train through intermediate wheels. Depending on the design, they move in jumps or continuously.
Where it comes from
The small seconds sub-dial goes back to 18th-century pocket watches. On pocket watches it usually sat at 6 o’clock, because that is where the fourth wheel was located. In other words, the position followed the layout of the movement. The arrangement lasted a long time. Before the Second World War, nearly every watch showed its running seconds on a sub-dial, usually at 6 o’clock.
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