Vintage Seiko RC-4000 S521-4010 PC Datagraph Computer Japan Digital Watch | WatchCharts
What is the identity of the mysterious watch that appeared in the auction as 'the ancestor of Apple Watch'? - GIGAZINE
Seiko RC-4000 - men's watch - Catawiki
My grandfather's Seiko RC-4000 watch from 1985. The "most advanced, hight tech" watch for its time that connected to the Apple II computer. : r/BuyItForLife
Fantastic 1980s Seiko RC-4000 Memo Digital Watch | #293103292