As the name implies, Cal. 23-300 is 23 mm (10 ligne) in diameter and 3 mm tall. This compact size made it ideal for the popular Patek Philippe Calatrava and similar smaller watches produced in the 1950's and 1960's.
Cal. 23-300 is classic in layout, with a barrel bridge covering the ratchet and crown wheel, a curved center wheel bridge, and separate cocks for the fourth and escape wheel. It was derived from the preceding Cal. 10-200 but with many modifications. It is notable in that it is equipped with both an overcoil hairspring and a free-spring Gyromax balance, a combination not found in any other 10 ligne Patek Philippe movement.
This movement is greatly respected today, with many saying it is one of the best hand-wound movements ever produced by Patek Philippe. Carlos Perez said it “represents both the technical and artistic peak of Patek's 10 ligne handwinds, as the 27-AM 400 was the peak of their 12 lignes.”
Cal. 23-300 was used in many watches, including the following popular references
- PP 10-200, the predecessor