The Black Watch is an electronic wristwatch launched in September 1975 by Sinclair Radionics. It cost £24.95 ready-built, but was also available for £17.95, as a kit.[These prices are equivalent to around £190 and £140 respectively in 2021, when adjusted for inflation.
The Black Watch was supplied with a plastic band as standard, with a black stainless steel bracelet available as an extra at £2.00.
I'm a fan of watches especially Texas Instruments, but when I come across watches like this 1975 Sinclair black watch I don't let it get away. Unfortunately he had problems with corrosion from the usual button cell batteries.
I solved, as often happens with objects with corroded pcb, to use 0.03 mm copper sheets. You have to clean up the damaged part and copy the part of the PCB to be reproduced on a transparent sheet, copy it on the copper sheet and cut it.
Then glue the pcb reproduced with silicone or with glue for gold leaf, I prefer the latter. Put it all together and you're done.
Wikipedia Sinclair Black Watch