8-day

An 8-day watch or clock is a manually-wound watch that can run for over a week without winding. These were often advertised using euphemisms for the week (Hebdomas, Huitaine) or the number 8 (Octo, Octus, Octomas). Although those registered brands were vigorously defended, many became common terms for the genre, notably huitaine, which means "about a week" in French.

8-day watches and clocks are referenced throughout the 19th century, though they were rare and likely not reliable. Alfred Courvoisier of La Chaux-de-Fonds advertised 8-day watches in 1859, Ulysse Perret of Renan produced springs suitable for these watches in 1865, Hattenberg of Le Locle promised a crown-winding 8-day watch in 1875, and more.

It was Irénée Aubry of Saignelégier who mastered long-running watches. He delivered a 40-day watch for Pope Leo XIII in 1887 based on a patent he submitted in Spain the year before and drew up his own 8-day watch patent, CH88, in November 1888. The Hebdomas caused a stir for its long power reserve but also for its novel design, with an open heart balance and decorated bridges below the offset dial. It was sold by Aubry and Arthur Graizely in the 1890s and produced in volume by Schild & Co of La Chaux-de-Fonds starting in 1913. The Hebdomas remains in production to this day.

Other firms, especially in La Chaux-de-Fonds, rushed their own 8-day watch designs to market in the 1890s to compete with Aubry. These included Charles Couleru-Meuri's Octo, Gindrat-Delachaux' Huitime, and many others.

Demand for 8-day watches eventually gave way to mass production of 8-day travel clocks, automobile dashboard clocks, and table clocks. Companies like Octo,

In modern times companies have returned to long power reserve movements, though often using double barrels. Jaeger-LeCoultre's limited-edition 1991 Reverso 70ème had 8 days of power from two barrels. IWC was one of the first to produce a modern single-barrel 8-day watch movement with their Cal. 5000, released in 2000.

Important 8-Day Watches and Clocks

• Hebdomas - An 8-day watch with an offset dial above an opening showing the balance and bridges invented by Irénee Aubry and marketed by Aubry, Arthur Graizely, and Schild & Co of La Chaux-de-Fonds
• Huitaine - An 8-day watch brand from Gindrat-Delachaux of La Chaux-de-Fonds and likely based on a movement designed and constructed by Charles Couleru-Meuri
• Octo - An 8-day watch with an open heart showing the running balance at 6 using a movement designed and produced by Charles Couleru-Meuri
• L. Rozat of La Chaux-de-Fonds advertised a patented 8-day watch in 1897
• C. Barbezat-Baillot of Le Locle advertised an 8-day movement in 1903
• Gindrat-Delachaux was advertising a different 8-day watch in 1906 and may have made complicated models with calendar, chronograph, and repetition
• Wyss Frères Octus brand appeared in the 1910s
• Zila produced an 8-day watch in the 1930s