Good to be reminded of the calculator - I bought one c. 1972 when still a student, I guess in relative terms it cost about the same as a basic laptop today. It was the second Sinclair Calculator, the first was a basic 4 function red LED display, a bit longer but slimmer, deep black, styled a bit like the monolith in the film 2001 which came out in 1968. Cost about £80. In styling terms perhaps it was the Apple of its day. A fellow student worked in a bookies office on Saturdays, was flush with money and bought one. I never knew why - his mental arthmetic was legendary: 2/6 to win at 7:2 ...answer in seconds. I wonder if currency decimalisation in 1971 was the big opportunity for calculators and for Sinclair, we did all the money stuff in 10's, not 12's and 20's after that.
I was on a science course with a fair bit of statistics involved: we could book and hour in the calculator room (a very special place with a few big desktop 4 function 4 memory machines, no printer so you wrote thinsg down), use a clunky mechanical adding machine or use pen, paper and a pale blue book of mathematical tables, logs and so on. That £50 calculator revolutionised all that, and not many months later you could buy cheap equivalents for less than £10.
If you are interested in such things, in Cambridge (off Coldhams Lane, not in the centre) is a museum of computing, lots of it 'hands on'. Worth a visit to bring back memories - or if you are younger, to marvel at how we managed to achieve anything with just 2k of RAM and no internet.
http://www.computinghistory.org.uk/
My view of Sinclair/Sugar is that Sinclair was a bit more of a 'blue sky' creative, Sugar was an adaptive creative who could develop existing ideas and market them. Each has their place.
(Someone mentioned Psion programmes, it was Psion Exchange: basic spreadsheet, word processor, charting programme and one or two other things, print module so you could churn out your report on a dot matrix printer - we didn't email pdfs back then)