What changed from the 3155
In 2015 Rolex unveiled the Day-Date 40 with the new Cal. 3255, replacing the long-serving Cal. 3155 after 27 years. The 3255 is essentially the day-date version of the simultaneously launched Cal. 3235, sharing its Chronergy escapement, 70-hour power reserve, and Superlative Chronometer ±2 sec/day rating. About 90% of the components are new versus the 3155, with 14 patents covering the escapement geometry, mainspring barrel, and stop-seconds mechanism.
Chronergy escapement
The Chronergy is Rolex's in-house refinement of the Swiss lever escapement, introduced first in the 3255 / 3235. Key changes: skeletonised nickel-phosphorus pallet fork (lighter, lower inertia), modified geometry of the impulse faces (about 15% better energy efficiency), and a longer power reserve as a direct result. The escape wheel is also nickel-phosphorus, made by LIGA process (a high-precision photolithography technique). The Chronergy is anti-magnetic and has been gradually rolled out across all current-generation Rolex calibers.
In every Day-Date 40 since 2015
The 3255 powers the Day-Date 40 across all metal variants: yellow gold ref. 228238, white gold 228239, Everose 228235, platinum 228206. The Day-Date 36 (smaller version, 128238 etc.) also moved to a 32xx-family movement (the Cal. 3235 with day disc, sometimes referred to as the 3255 simply by Rolex naming convention). The 3255 is exclusive to the Day-Date line; the 3235 covers the 3-hand date watches (Datejust 41, Sub 41, etc.).
The day disc, in 26 languages still
A continuity feature: the 3255 retains the option of 26 different language day discs, the same option Rolex has offered on the Day-Date since 1956. Customers can specify Spanish (DOMINGO/LUNES), Italian (DOMENICA), Arabic, Greek, Hebrew, Roman numerals (DIES SOLIS / DIES LUNAE), and many others when ordering. Most boutique stock is English; the exotic discs are made to order. The day-change is instantaneous at midnight, an upgrade from the slow change of the 3155.
Where it sits
The 3255 is the current top-of-the-house automatic in the Day-Date line, exclusive to Day-Date models in precious metals. With the Superlative Chronometer rating of ±2 sec/day (chronometer-grade is normally -4/+6), Parachrom Bleu hairspring, Chronergy escapement, and 70 h reserve, it is technically the most capable mass-production day-date movement on the market. Service intervals at ~10 years; full service through Rolex Service Centre runs USD 1,200-1,800 depending on case material.
