A tide indicator is a watch complication that shows when the next high and low tides will come. The wearer sets it once for their own stretch of coast. After that it keeps track of the tides by itself, with no further adjustment.
How does a tide indicator work?
The tide cycle runs a little longer than half a day. On the Heuer Mareographe, a subdial at 9 o’clock shows the next high and low tides. Its high and low tide marks sit 12 hours 25 minutes apart, not 12 hours. A US patent describes a ring-shaped wheel that turns once for each cycle of two high and two low tides, which takes 24 hours 50 minutes. In the IWC Portugieser Yacht Club Moon & Tide, the display takes its power from the hour pinion of the base movement. A reduction gear slows the tidal disc to one turn in exactly 14.76 days.
Does a tide indicator work on every coast?
Not always. The IWC display works reliably only on coasts that have two high and two low tides of equal strength each day. On coasts with a different pattern, its reading cannot be trusted. The strength of the tide also changes through the month. Spring tides, the strongest, come at full moon and new moon. The weaker neap tides fall between them. Some tide indicators show this strength as well as the timing of high and low water.
Where it comes from
Heuer brought out its tide-indicating chronographs in the early 1950s. Before them came the Solunar, which showed only the time and the Moon’s progress through the lunar month. Heuer then paired a tide display with a chronograph built on a Valjoux base, and this became the Seafarer. Most of Heuer’s tide chronographs were sold under the Abercrombie & Fitch Seafarer name. On the modern TAG Heuer Seafarer, the tide disc is geared to turn once every 29.53125 days. That is close to the average lunar month.
Not to be confused with
The term ‘tide dial’ can mislead. It names something different: a medieval sundial marked with the canonical prayer hours. That is not a watch, and it does not show the tides of the sea. A watch complication that shows when high and low tides will come is a tide indicator. It is set for the wearer’s own location and then keeps turning on its own.
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