Hi, for all things Sinclair, including audio and calculators as well as the more well known home computers, see this website:
http://www.nvg.ntnu.no/sinclair/contents.htm
On this site you can find some of the original adverts for the Sinclair products, it seems Sir Clive 'slightly over exaggerated' the specs and performance figures for some of his products,
allegedly.
I have posted this link before, elsewhere on the forum, but on an unrelated subject matter.
Cheers,
Baz