"Hmm...How can I make a sideview LED style digital watch and still be mechanical? I got it! Make two dials for hour and minutes, print the numbers backwards and have a prism reflect the corrected mirror image through the side crystal."
- Likely thoughts of Swiss mechanical digital inventor Joseph Bamat when creating the 1970's Amida Digitrend mirrored prism jump hour digital mechanical watch. (also made by Crehor & Hudson)
Patent information describes it in further detail;
DIGITAL WATCH (filed November 1970)
A timepiece includes a pair of rotatable discs carrying respectively hour and minute indicia on one surface adjacent their peripheries. The indicia are arranged to pass, on rotation of the discs, adjacent the geometric central axis of the case of the timepiece. A window is formed at a position corresponding to the geometric central axis of the case, in a cover of the case, for viewing the indica.More photos here