Complication · Calendar & astronomy
Running Equation of Time (Equation Marchante)
Partially verifiedA display using two minute hands: one for mean time and one for solar time.
Definition
A display using two minute hands: one for mean time and one for solar time.
Historical origin
Invented in the eighteenth century by French makers (notably Lepine and Berthoud) to show the difference between sundial and clock time directly.
How it works
Two concentric minute hands are used.
One is driven by the regular train; the other is driven by an equation cam that offsets it relative to the first.
Pocket watch context
A prestigious feature in late eighteenth-century French pocket watches.
Wristwatch context
Rarely seen today except in high-art horology from brands like Breguet or Blancpain.
Identification
- Two minute hands, one often carrying a sun symbol
- Differential gearing visible under the dial
Servicing notes
Requires precise alignment of the equation cam to the calendar work.
General guidance only. Complicated mechanisms should be assessed and serviced by a qualified watchmaker or clockmaker specialist, not adjusted at home.
Diagram
Sources & references
- de Carle, D., Watch and Clock Encyclopedia
- Britten, F. J., Old Clocks and Watches and Their Makers
- Horological Journal (British Horological Institute), technical articles
Where sources disagree, the disagreement is stated rather than resolved silently.