Portal:Anniversaries/December 31: Difference between revisions
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- Occasionally — A "leap second" can be added at any time, but the IERS prefers to add one on June 30 or December 31. One is needed about every 20 months.
- 1999 — Zenith stops supplying the El Primero chronograph movement to Rolex, interrupting supply of the popular Cosmograph Daytona model.