Winter poses a number of issues to your watch wearer — practical, sartorial and at times technological issues. Similar to the ref. 6536 above, it was readily available in both chronometer and non-chronometer variants, but this was The 1st time the COSC watches really experienced the 'Formally Accredited Chronometer' text https://www.watchesworld.com/frozen-in-time-luxury-watches-for-winter/