Sinclair digital 'Black Watch' kit, 1975.

The 'Black Watch' was launched in September 1975 and was available for £17.95 in kit form or £24.95 ready-built. The creation of Sinclair Radionics Ltd of St Ives, Cambridge, it was made of black plastic with a five-digit LED display. It was of a curious design without any buttons - instead, it had two panels which turned on the display for a couple of seconds, showing either hours and minutes or minutes and seconds. Unfortunately, the watch was a commercial failure, nearly bankrupting the Sinclair company. The kit was difficult to construct (and once built was too easily damaged), the quartz accuracy was susceptible to temperature change, and the batteries ran flat after only ten days, or, worse still, were liable to explode if the display malfunctioned and didn't turn off.