The steel reference 5212A Calatrava Weekly Calendar not only introduces an entirely new complication to Patek Philippe’s collection but in addition introduces a completely new case design and a highly unusual and unique dial. The present watch is only the third example of the reference to be offered at international auction and is accompanied by the full set of accessories. Reference 5212A was launched in 2019 and only produced in stainless steel. It is the first and only watch with this complication to be made by Patek Philippe and sports a distinctly retro look with its ‘hand-written’ style of dial and stepped curved lugs. Intended for the modern business person, the calendar movement is calibrated to calculate the day, month, and the week according to the ISA 8601 standard. This system means that the first official week of the year starts on the Monday of the week of January 4. The weeks are numbered in accordance with the ISO 8601 standard, which states that the first full week in any year must begin on Monday, not Sunday, and that the first full week of the year is that which contains January 4. A feature of the standard is that occasionally a year will contain 53 rather than 52 weeks, which is accounted for in the calendar mechanism and numbering scheme on the dial. The ISO 8601 business calendar was founded by the International Organization for Standardization for use mainly in the international financial sector. It is a purely numeric calendar whereby the number of the week within the year and the number of the day within the week are used in place of named months and days. This globally recognised format transcends any cultural ambiguity possible in other calendars. The fascinating dial typography is unique for a Patek Philippe watch and is, according to the company, based upon the handwriting of one of the watch’s designers. The date is displayed in the date window at 3 o'clock, the day of the week is indicated by the inner hand with flat red tip, and the week and month around the edge of the dial are indicated by the similar longer hand.