sinclair cambridge programmable

this was my first programmable calculator (this is actually it!) from 1977. sinclair burst onto the calculator scene in the early 70's offering cost effective alternatives to the models of hewlett packard and texas instruments. this was their first programmable.

it was amazing for its time, a 36 step programmable memory (volatile) in which many tricks could be used to save space. since each key press cost a step, they represented their shifted function in program mode (ie the function written above). to program numbers you must precede input with the # character (which costs a step). another trick is that the program will run round from step 35 to step 00, often saving a jump.

it has one conditional branch, goto if neg, from which any test may be determined by careful program re-arrangement.

it came with a program library consisting of 4 books. each covering different subjects:

  1. general/finance & stats
  2. mathematics
  3. physics & engineering
  4. electronics

the library programs were well written and managed to extract a great deal of functionality out of the, otherwise limited, machine. later, sinclair superseded this model with the enterprise. but, by then more sophisticated programmables were available at reasonable cost.

i discovered experimentally, that pressing divide would interrupt program execution and display the current value, thereafter run could continue execution (as far as i know this is not documented). this new feature enabled me to write a whole new range of interesting programs; dice throwing, random numbers, a stopwatch timer and games like whack a mole.


the machine is powered by a 9v pp3 battery and consequently had a pregnant bulge at the back. nevertheless it remains very pocket sized and thumb useable. the construction is rather cheap and the buttons click. however, it can survive a fall from a window by exploding apart into separate pieces that simply click back together leaving the unit totally unharmed (if it doesnt, dont blame me).

despite click buttons, they didnt tend to contract the incurable bounce problems of ti models. if you have one that bounces intermittently, try pressing it quite hard with your thumb. this often fixes it.