Sinclair's LED watch was launched in September 1975 at 17.95 in kit form or 24.95 assembled. As well as being descriptive (the majority were all-black although there were a few produced in grey and white), it is a pun on the Black Watch Scottish regiment.
The watch had a 5-digit display and concealed buttons on the front to display hours or minutes and seconds. Some had a calendar option. The time only displayed for a few seconds after a button press to save power. Even so, batteries only lasted about 10 days.
Although quite stylish to look at, they were notoriously unreliable, and the time-keeping was very temperature-dependent. Many thousands stopped working and were returned at great cost to Sinclair which made a loss on the product. The kits were also very difficult for the amateur to assemble. Consequently, very few working watches survive today.
Battery compartment in rear. Button is for setting the time.
Display case and instructions.