Cambridge - Vintage Sinclair

Sinclair launched the first in a range of Cambridge models in August 1973. They weighed less than 3.5 oz, cost £43.95 and measured just 50 X 111 X 28mm. The first models were basic 4-function calculators but later, scientific and programmable models were released, ending in the Cambridge Universal, produced up until late 1977.

This model came in 4 incarnations - Type 1 to Type 4.
Most took 4 X AAA batteries (6V), but the later ones had a 9V PP3 battery for longer life.
The Type 1 and Type 3 had K (constant) keys.
Type 2 had C and CE keys.
Type 4 had % key. It is also the rarest of the Cambridge range, presumably because by 1977 ,the design was 4 years old and LCD calculators from Japan were becming available and so relatively few were sold.

All came in a polystyrene-lined box with plastic carry case and instructions.
These explained how to do constant arithmetic and reciprocals, and had examples of how to perform currency conversions, mortgage interest repayment, and compound interest.

Cambridge Memory

This model came in three variations - Type 1, Type 2 and Type 3.

The Type 1 took 4 x AAA batteries, had 4 functions and an RM/CM key (one press recalled from memory, two presses cleared the memory).
The Type 2 took 2 x AAA batteries, and in addition to the Type 1 abilities, had a % key.
The Type 3 took a 9V PP3 battery, and had M, C/CE and % keys. The rear of the case had to have a bulge to accommodate the large battery.

Cambridge Scientific

Launced in March 1974 at a cost of £49.95, it was a development of the Cambridge with the same case but the addition of some scientific functions such as logarithms, trig, square root and pi.
Took 2 X AAA batteries and there was a switch to select degrees or radians inside the battery compartment.

Cambridge Programmable

On 1st September 1976, the Cambridge Programmable was released (marketed in the United Sates as the Radio Shack EC-4001).
It had an 18 byte memory allowing a 36-step 'program' to be entered. However it came with an impressive 4 volume set of program libraries!
It took the larger 9V PP9 battery which resulted in the bulge at the rear (below).

Cambridge Universal

4-function, %, memory, square, square root.
Also had the bulge at the rear to accomodate the 9V battery.