TW Factory Jaeger-LeCoultre Master Calendar 1558420 Cal.866
The TW Factory Jaeger-LeCoultre Master Calendar 1558420 is an automatic mechanical calendar watch combining day, month, date, and moonphase indications within the classic Master Calendar dial layout.
At 12 o’clock, two separate apertures display the day of the week and month, while the lower section of the dial incorporates the moonphase and date indications.
The watch uses a Cal.866 automatic mechanical movement, sapphire crystal on both the front and caseback, and an Italian calfskin leather strap with a folding clasp.
Master Calendar Dial Architecture
The defining characteristic of the Master Calendar 1558420 is its balanced multi-function calendar layout.
Instead of concentrating all calendar information within a single subdial, the different indications are distributed across the dial.
The principal functions include:
* Hours
* Minutes
* Seconds
* Day of the week
* Month
* Date
* Moonphase
This arrangement provides considerably more calendar information than a conventional date watch while maintaining clear separation between the individual indications.
Day and Month Display at 12 O’Clock
Two rectangular apertures are positioned at 12 o’clock.
One displays the day of the week, while the other displays the month.
Placing both indications together at the upper section of the dial allows the wearer to reference the main calendar information without interfering with the central time display.
The symmetrical positioning of the two apertures also forms an important part of the Master Calendar’s visual identity.
Moonphase Display at 6 O’Clock
The moonphase indication is positioned at 6 o’clock.
This lower display provides a visual representation of the moonphase and balances the day/month apertures positioned at the top of the dial.
The result creates a vertically organized calendar layout, with the day and month above the central hands and the moonphase below them.
Date Display
The watch also incorporates a date indication around the lower calendar display.
This allows the Master Calendar to present the day, month, date, and moonphase information together on a single dial.
The date function forms part of the broader calendar architecture driven by the automatic mechanical movement.
Cal.866 Automatic Mechanical Movement
The TW Factory Master Calendar is equipped with a Cal.866 automatic mechanical movement.
The movement is configured to operate the primary timekeeping functions together with the watch’s calendar indications.
These include the day, month, date, and moonphase displays.
Automatic winding allows normal wrist movement to contribute energy to the movement during regular wear.
Sapphire Crystal
The front of the watch uses a sapphire crystal.
Sapphire provides a hard, transparent surface over the dial and allows the multiple calendar indications to remain clearly visible.
Sapphire Exhibition Caseback
Sapphire crystal is also used on the rear of the watch.
The transparent caseback allows the mechanical movement to remain visible from the reverse side, adding another visual element to a watch whose front dial already emphasizes its mechanical calendar functions.
Italian Calfskin Leather Strap
The Master Calendar is fitted with an Italian calfskin leather strap.
The leather construction complements the traditional appearance of the Master collection while maintaining a softer and more flexible contact surface around the wrist than a metal bracelet.
Folding Clasp
The leather strap is secured with a folding clasp.
The clasp construction reduces the amount of repeated bending required when putting on or removing the leather strap and provides a secure closure during regular wear.
Technical Specifications
Specification Details
Factory TW Factory
Brand Jaeger-LeCoultre
Collection Master Calendar
Reference 1558420
Movement Cal.866
Movement Type Automatic Mechanical
Hours / Minutes Yes
Seconds Yes
Day Display 12 o’clock
Month Display 12 o’clock
Date Display Yes
Moonphase 6 o’clock
Front Crystal Sapphire
Caseback Sapphire Exhibition Caseback
Strap Italian Calfskin Leather
Clasp Folding Clasp
Calendar Display Structure
The 1558420 differs from simpler Master models primarily through the amount of calendar information incorporated into its dial.
The day and month apertures at 12 o’clock provide immediate calendar references, while the moonphase and date indications occupy the lower portion of the dial.
Separating these functions between the upper and lower sections helps prevent the calendar information from competing visually with the central time display.
This layout is one of the most recognizable technical and visual characteristics of the Master Calendar.
Cal.866 and Calendar Functions
The Cal.866 configuration brings the different indications together within one automatic mechanical system.
The primary hands provide conventional timekeeping, while the movement simultaneously supports the day, month, date, and moonphase displays.
This makes the movement architecture substantially more function-oriented than a basic three-hand or date-only mechanical configuration.
Wearing and Care
The Master Calendar incorporates several mechanically connected calendar functions, so adjustments should always be performed carefully.
Avoid forcing the crown or calendar adjustment mechanisms if unusual resistance is encountered. Calendar adjustments should also be performed according to the intended setting procedure to reduce unnecessary stress on the movement.
The Italian calfskin strap should be protected from prolonged exposure to water and moisture.
Strong impacts and powerful magnetic fields should also be avoided.
Frequently Asked Questions
What is the reference of this TW Factory Master Calendar?
The supplied reference is 1558420.
What movement does this version use?
It uses a Cal.866 automatic mechanical movement.
What calendar functions does the watch have?
The watch incorporates day, month, date, and moonphase indications.
Where are the day and month displayed?
The day and month are displayed through two separate apertures at 12 o’clock.
Where is the moonphase displayed?
The moonphase indication is positioned at 6 o’clock.
Does the watch have a date display?
Yes. The date indication is integrated into the lower calendar display area.
Does it use sapphire crystal?
Yes. The supplied configuration uses sapphire crystal on both the front and rear of the watch.
Can the movement be seen from the back?
Yes. The watch has a sapphire exhibition caseback, allowing the mechanical movement to be viewed.
What type of strap does it use?
It is fitted with an Italian calfskin leather strap.
What type of clasp is fitted?
The watch uses a folding clasp.
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