The IWC Portugieser Eternal Calendar’s 45-million-year claim applies to its moon-phase display—not to the watch’s overall timekeeping. IWC calculates that the display will drift by one day relative to the moon after 45 million years; Guinness World Records lists the more precise figure as one day in 45,361,055 years. Separately, the watch’s secular calendar is designed to handle Gregorian century-year leap-year exceptions through at least 3999.
What does the 45-million-year figure measure?
It measures the calculated error of the moon-phase display. A moon-phase indication represents the cycle from one new moon to the next, which IWC gives as 29 days, 12 hours, 44 minutes, and 2.88 seconds. The Portugieser Eternal Calendar uses a reduction gear between the calendar movement and moon-phase disc to approximate that cycle.
IWC’s 9 April 2024 launch release says the display will deviate from the moon’s orbit by one day after 45 million years. Guinness World Records gives the more exact result as one day in 45,361,055 years and names the watch the “most precise lunar phase wristwatch.” Guinness lists 30 April 2024 as the record date and says it validated the record on 10 June 2024. That is a theoretical calculation, not a watch physically tested for millions of years.
The distinction matters: this figure does not say that the watch will keep perfect time, remain reliable, or run without service for anything like that duration. It describes the accumulated deviation of one display from the lunar cycle.
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How does the secular calendar handle leap years?
Introduced on 9 April 2024 as reference IW505701, the Portugieser Eternal Calendar is IWC’s first secular perpetual calendar. It tracks month lengths and the usual leap year every four years, while also accounting for the Gregorian calendar’s century-year exception: a century year is not a leap year unless it is divisible by 400.
That means 2100, 2200, and 2300 are common years, while 2000 and 2400 are leap years. IWC says the mechanism is designed to calculate leap years correctly through at least 3999. The status of 4000 has not been officially decided, according to IWC.
The 400-year gear
A new module checks for the four-year leap cycle at the end of February. A gear makes one revolution every 400 years; its three indentations skip the three century-year leap years that the Gregorian rule omits in that span. IWC describes the gear as an eight-part component.
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The calendar module builds on IWC’s existing modular, synchronized perpetual-calendar design. IWC says its displays can be advanced using the crown. These are manufacturer descriptions of the mechanism, not independent observations of the watch in use.
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How was the moon-phase gearing calculated?
The reduction gear uses three intermediate wheels to translate the calendar movement into the moon-phase disc’s slower cycle. IWC says its engineers selected the gear train after computer simulations of more than 22 trillion combinations in the 9 April 2024 launch release. In a separate 26 June 2024 record announcement, IWC described almost 23 trillion combinations. Those are the figures stated in the respective releases, rather than one combined exact count.
The June announcement also describes the wheels as made using LIGA manufacturing. IWC’s account explains the engineering basis for the precision claim; the Guinness listing records the result, but neither should be read as a long-duration physical test of the watch.
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- Silicone watch strap soft and dust-resistant , comes with a quality stainless steel buckle, which is made of stainless steel.
- Please measure the width of your watch lug before ordering. It is important that your watch's lug width is the exact width of the band you select.
- Softness is moderate, wear very comfortable,Compression molding, sturdy and ,Wearable strap/wrist strap,suitable for original watch.
- Comfortable Fit: Soft, skin - friendly rubber conforms to wrist curves. Multiple adjustment holes ensure a perfect fit for all wrist sizes, offering stable, non - tight wear.
- Easy to insert and remove,very suitable for your watch.
What else distinguishes reference IW505701?
IWC specifies a platinum case, a glass dial, double box-glass sapphire crystals, and a black Santoni alligator-leather strap with a platinum folding clasp. Its Double Moon indication shows lunar phases for both the Northern and Southern hemispheres. These are specifications published by IWC, not hands-on findings.
For the mechanism and product details, see IWC’s 9 April 2024 launch release, its 26 June 2024 record announcement, the Guinness World Records listing, and IWC’s current Eternal Calendar complication page.
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