Thanks for your interesting video review.
All kudos to the engineers who were able to cram so much into such a tiny space; without SMD parts, it may look primitive to the
Arduino Generation, but everything about this calculator, including the LED digit display, was cutting edge (most calculators where using vacuum tube displays). I note the PCB has the look of being designed by hand, with cut tape and sticky pad stencils. Now that's real layout skill.
I remember one of my father's engineering colleagues having one of these. From the vintage calculators website, I think it was a Cambridge model 2 or 3 in white. The Sinclair was not much of a threat to the engineers slide rule, but was way cool and a must have for all striving executives (and accounts).
http://www.vintagecalculators.com/html/sinclair1.htmlAs a vintage fan, I thought you might be interested in this Sinclair advert in an ancient Wireless World magazine from June 1977. Although rather lacking in functionality (even for that time), a
wrist calculator was something from the Space Age. Respect to anyone who managed to solder one of these together.
For those "playing at home", £11 sterling in 1977 in today's money is ~ £70 ($132AUD/$90USD/80EURO). At time of posting, there's an uncompleted kit on ebay, collection only, for an eye watering £2,350! Compare this to the price of an apple watch.