Specifications:

• automatic movement calibre 852x with Pellaton winding mechanism
  • IWC inhouse production
    • calibre 852: without date indication
    • calibre 8521: with date indication
  • diameter: 28.8 mm
  • height:
    • calibre 852: 5.6 mm
    • calibre 8521: 6.40 mm
  • number of jewels: 21
  • frequency: 19,800 A/h = 2.75 Hz
  • balance spring: Breguet
  • fine adjustment: classic regulator
  • shock resistance: Incabloc
  • total production (only a small part used in Ingenieur models)
    • calibre 852: ca. 50,400 pieces
    • caliber 8521: ca. 13,200 pieces
• tripartite screwed case, water resistant to 10 atm
  • middle part of case: satinised
  • top part with bezel: polished
  • bottom part polished with six recesses (for screwing tool), central circle satinised
  • amagnetic to 80,000 A/m, movement protected by Farraday's cage made of soft iron inner case and soft iron dial bottom
  • glass: Plexi
• case number between lower lugs (not as usual on case back)
• Ingenieur-Logo above index at 6
• straps & bracelets
  • leather
  • ...

In 1959, the Ingenieur benefited from an enhanced version of the IWC automatic movement. The new calibre 853/8531 represents a natural evolution of the calibre 852/8521, incorporating relatively minor improvements on the balance wheel and the barrel. In a time where the date function was somehow a standard fit on automatic wristwatches, the calendar version became far more popular and the ref. 666 AD wastly outsold the non-date ref. 666 A. In the early sixties, some more dial varations were introduced. Various types of gold and steel bracelets were now regularly offered in the catalogues, as there was an optional magnifying lens over the date window.

But despite these minor adjustments, the Ingenieur remained essentially the same watch as it was when first introduced in 1954/55. Even as the new improved version of the automatic calibre 854x was introduced in 1963/64, IWC felt no urgent need to update its successflul flagship. As one of the last surviving models still equipped with the old calibre 853x, the ref. 666 was phased out as lat as 1966/67 to be replaced by the new ref. 866.

 
Specifications:

• same movement and case as above for «reference 666 with calibre 852x»
  • movement: calibre 853x featuring improved barrel and equalizing screws on balance
  • total production (only a small part used in Ingenieur models)
    • calibre 853: ca. 91,200 pieces
    • calibre 8531: ca. 48,200 pieces
• straps & bracelets
  • leather
  • steel Type «beads-of-rice» by Gay-Frères, end of fifties/beginning of sixties
  • steel and gold: Reference 11, mid sixties
  • gold: Type «brick», end of fifities/beginning of sixties