In August 1975 Sinclair introduced the Black Watch digital watch at £17.95 in kit form and £24.95 ready-built, although this wasn't available to buy until January 1976. Including a five-digit LED display, it suffered from technical flaws related with the design of the case, the chip, the battery and accuracy. Not only was the watch unreliable, Radionics was not able to fulfil the orders it had taken. As a result, Radionics made its first loss in the financial year April 1974-April 1975. The Black Watch fiasco had a devastating effect on Sinclair's finances and the company would have gone bankrupt had not the Government, through the National Enterprise Board (NEB), stepped in to support it.
en.wikipedia.org/wiki/Sinclair_Radionics
en.wikipedia.org/wiki/Black_Watch_(wristwatch)

This specific watch was sold to its first owner on 14-09-1976.

The Black Watch on Sinclair Research Ltd's website:
sinclairzx.com/about-us.html#7

Planet Sinclair:
nvg.ntnu.no/sinclair/other/blackwatch.htm

Popular Mechanics Dec 1975:
books.google.ch/books?id=MOIDAAAAMBAJ&pg=PA125&lpg=PA125&dq=sinclair+black+watch+battery+type&source=bl&ots=iWyofSMWtB&sig=U9EQfyMa_XPK2ZSgh6xOcNiEmBM&hl=en&sa=X&ei=Bfg9UbejFIPZPO3mgfAK&ved=0CFwQ6AEwBA#v=onepage&q=sinclair%20black%20watch%20battery%20type&f=false

Popular Science Jun 1976:
books.google.ch/books?id=CgEAAAAAMBAJ&pg=PA149&lpg=PA149&dq=sinclair+black+watch+battery+type&source=bl&ots=FR8BRbhnUP&sig=YeO5AeZn-a3kUKe5DHePDi8bVHM&hl=en&sa=X&ei=Bfg9UbejFIPZPO3mgfAK&ved=0CGYQ6AEwBg#v=onepage&q=sinclair%20black%20watch%20battery%20type&f=false

Forum entries:
dwf.cc/viewtopic.php?f=37&t=96
dwf.cc/viewtopic.php?f=35&t=539

Sinclair related picture gallery:
skydrive.live.com/redir?resid=C250D8748980CE5A!2656&authkey=!9TR9Dy4oJWc%24

Music is track Nuclear Clock by Musicshake.

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