Audemars Piguet might in fact have made not just the gongs however, the entire motion: in those days, it was common for European watch companies to buy raw motions from Swiss companies and finish them for their own specifications.The watch[...]
Now this view is available since the Datograph Auf/Ab; the movement was improved and a power-reserve screen has been added. There’s also a variant with a perpetual calendar, the Datograph Perpetual.The Lange 31 has been named for its power book:[...]