In reply to aiden.

Although Rolex did not own Aegler outright until 2004, they were still designing and engineering the movements before purchasing the manufacturing facilities. By contrast, many microbrands today use off-the-shelf movements from various manufacturers (often either ETA, Sellita, Seiko, or Miyota). However, these movements are not of their own designs and they are used in many different watches from other brands (ie. you will find watches from countless brands fitted with the ETA 2824 movement). However, Rolex's in-house movements are actually in-house creations and as such, they are not found in any other brand's watches (ie. the Rolex Cal. 3135 will only be found inside Rolex watches).