Today's watch was a gamble to buy as I'd seen that it was part of a pile of junk, but didn't expect it to work.
The watch is called The Black Watch and was made by Sinclair. Actually, it wasn't necessarily made completely by Sinclair as it was sold in two ways - either as a complete watch, or as a kit for you to make yourself. It was released in September 1975 and cost £24.95 ready built or £17.95 for the kit.
It has a 4 digit LED display at the top of the case, and is a very minimal design. The buttons are hidden in the middle section and seem to show either hours and minutes (by pressing the left side), or minutes and seconds (using the right side). The design was described in the adverts as being "styled in the cool prestige Sinclair fashion: no knobs, no buttons, no flash". It is powered by two LR44 batteries which could be accessed by a plastic flap on the back. By default, it came with a black leather strap, but you could get a luxury stainless strap as an extra. The watch should have a sinclair marked plate surrounding the LED display, but that is missing from my watch.
The watch is quite a rare and collectable watch as they weren't very robust, and could be rendered useless by the static from a nylon shirt or even air conditioning. The watch was a major failure because of that problem, and other problems with production (from the same static issue as above), temperature sensitive quartz crystal (which changed the speed between summer and winter), exploding batteries, control panel failures, 10 day battery life, constructability issues for the kit (despite the claims that anyone who can use a soldering iron can make it), and a case that couldn't be glued (so would often fall apart when the clips didn't work). These problems lead to massive returns and a 2 year replacement backlog, and resulted in Sinclair losing so much money they were only saved from bankruptcy by government subsidies.
Sinclair (or Sinclair Radionics to give them their full name) was founded in 1961 by Sir Clive Sinclair and started with radio products, making the world's smallest FM radio of the time. In the early 70s they moved into calculators making much smaller and styled units than the competitors and leading to a major success. In the late 70s, after the financial troubles from the black watch, Sinclair has started a new company called Sinclair Research which produced the most famous Sinclair product in 1982, the ZX Spectrum home computer. Sinclair also had another marketing disaster in 1985 with the Sinclair C5 electric vehicle, which was deemed impractical to use in the UK, but was still the biggest selling electric vehicle in the UK until the Nissan Leaf overtook it in 2011.