this model dates back to 1974 at a time when sinclair was
introducing affordable pocket calculators. back then, if you wanted a
scientific calculator, it costed!. from 1972 you could buy a hp35
for $395 (a fortune then) and it wasnt until 1974 that texas instruments
introduced their scientific sr-50 for $169.95.
the scientific functions offered by this model are somewhat
approximate. the machine is fixed at 5+2 digits and you are lucky to get 4
digits correct. furthermore, there are no input checks to bring trigs into
computable range. you have to do this manually. there are no other
functions, like powers, roots or even a memory. some handy constants are
written on the face for reference.
despite these shortcomings, the machine was useful. at a time when
other scientific models were prohibitively expensive it beat using a slide
rule. its low cost and small size were possible because, the main
component was not itself natively scientific. amazingly, sinclair managed
to use parts of the main logic in new ways to implement scientific
by comparison, the hp35 had a small processor
with rom microcode to implement scientific functions through cordic
this model is powered by 4 AAA cells, which gave a smoother profile
than the later (pregnant) models and typically came in a hard plastic case
that protected it. if you have one of these, ensure that the battery
connectors are straight as they sometimes fall out of line and cause the
infamous hot battery problem!