Sinclair Cambridge, the first in a range
of seven calculators, was launched in August 1973.
It was small, even by today's standards, weighed
less than 3.5 oz and sold at £29.95 + VAT
or, in kit form, at £24.95 + VAT. A "valuable
book" [sic] was supplied with it to explain
how to use the Cambridge to handle advanced functions
such as trigonometry, nth root extraction,
compound interest and the like.
months later in March 1974, the Cambridge Scientific
was launched at a price of £49.95 (£5
cheaper than its nearest rival from Hewlett-Packard).
As the name suggests, it was a development of
the Cambridge, using the same case, with the addition
of a number of common scientific features (sin,
cos, tan etc).
The other calculators
in the range comprised the Cambridge Memory,
Cambridge Memory % (which came in two different
versions), Cambridge Programmable (marketed
in the United States as the Radio Shack EC-4001),
Cambridge Scientific, Cambridge Scientific
Programmable and Cambridge Universal.
The later Sinclair
Scientific first appeared in a
case derived from that of the Cambridge, but it
was not part of the same range.
The Cambridge calculators
suffered from a near-fatal design flaw which resulted
from the cheapness of the components - after some
use the calculator would be impossible to switch
off. This resulted from the material used to make
the switch contacts. Most circuit board connectors
are made of gold-flashed nickel (the Spectrum
edge connector is a prime example) and the prototype
Cambridge was no exception. However, when full
production began, it was decided to make use instead
of cheaper tin-coated nickel connectors. This
grew a soft oxide layer (not a problem with gold,
which doesn't oxidise), with the result that after
the switch had been slid backwards and forwards
a few times the surface of the tin would smear
across the insulation so creating a permanent
circuit. Having to take the battery out to cut
the power every time one had finished using the
calculator was, to say the least, inconvenient.
with all of the Sinclair calculators, the Cambridge's
display used light-emitting diodes. This made
it a power-hungry device, forcing a rather messy
design compromise on the Cambridge Memory % Type
2 and Cambridge Programmable. The power demands
of both devices required the use of a PP3 battery,
creating the distinctive "pregnant"
appearance of the case (right).