Retro Review: Sinclair Enterprise Programmable Calculator (1977)

I had great fortune recently finding this little gem on the excellent Oxfam Online Shop, which I heartily recommend you check out.  You never know what hidden gem you may discover  from the 165 nationwide stores that are listing, and over 100,000 items in total to choose from.


I’ve been lucky enough to own a few Sinclair calculators in the past, but this is my first Enterprise.  Released in 1977, the 8-digit LED scientific programmable calculator was based around a single transistor and three National Semiconductor chips, namely the MM57146AEG/N, MM57126N and DS8874N.  Measuring 65mm x 135mm x 23mm and running on a 9v PP3 battery, the Enterprise cost around £25 in 1978.  We know this model was purchased in a Branch of Boots the Chemist on 4 November 1978 (maybe an early Christmas present) … I won’t say where, but let’s just say ‘oop North!’

There was another (non-programmable) Enterprise with a bigger LED array, but other than the lack of programming functions it was fundamentally the same.


As we know from history, stuff built in the seventies in the UK was generally rubbish (think of ‘Buckaroo’ and British Leyland).  The screws inside the Enterprise look like they’re made of zinc, and somehow (but the mercy of God, probably), they haven’t corroded into a pile of mushy metal.  There was a charming story about the Sinclair Black Watch.  The watch itself was so badly made, that more often than not the casing itself wouldn’t hold together.  The plastic used was unglueable, and it was redesigned in order for the shell halves to be clipped together.  This didn’t work, so Sinclair gave up and subbed the whole thing out to a contractor.  Much later on, Sinclair received a Black Watch in the post with a note from the Contractor saying “We’ve sorted the problem!”  Inside the packaging was a Black Watch with a half-inch bolt through it!

To change the battery, you have to take off the entire front of the calculator!









I’ve seen another Enterprise elsewhere online with a serial number very close to the one I have, produced a year earlier.  I’m guessing this meant they didn’t manufacture them very quickly, despite the poor quality of the construction.



Sinclair design was always a favourite of mine, from the Microvision TV to the hifi equipment they briefly made and, of course, the Black Watch and other calculators in the range (we’ll forget the C5, alright?)  The stark black and white casing and keypad, with the sinister red plastic and LED array were just something else.



There’s a socket on the side for the 9v DC adaptor, which was thankfully included with my purchase.  Boxed too, which was a nice touch.

P1000236 P1000237


The calculator was shipped with the ubiquitous 70s and 80s leatherette pouch!



This is probably the most complete calculator I’ve ever owned.  The paperwork that accompanied it was astonishing, starting with the original Guarantee slip.  I’ve Photoshopped out most of the address.



Here’s the READ THIS FIRST! leaflet that also accompanied it.  This little sheet quickly shows you how to program the calculator, with key input commands showing you how to convert centigrade to fahrenheit, and how to calculate mortgage repayments.  To prove just how old this thing is, it calculates an £8,500 mortgage at an interest rate of 11% over 25 years.  (It’s £84 a month if you haven’t already worked it out on your iPhone!)

The Operating Instructions Manual is printed on thin paper but runs to 44 pages.  That’s included too.



The most interesting part of the collection despite the calculator is the three-volume Program Library.  These edge-screw bound cards help you program everything, from random number generator to intercepts of a line, mortgage repayments to resistors in parallel calculations.  All three volumes are completely intact and a very nice addition.

P1000242 P1000243 P1000244


Finally, and not something that would have been shipped with the calculator, is a curious little black book entitled Pocket Reference Tables.  The leatherette covered book has ‘For Private Circulation’ printed in gold script on the cover, a gift (reasonably obviously) from the ‘Short Loan & Mortgage Co Ltd’.  It includes pages of calculation charts for Loan Charges, Changes in the Bank Rate since 1929 and Interest Rates.  Some hand-written notes inside the book make me believe the book dates from 1965.  It’s definitely pre-decimal.  It belonged to Mr Charlton, as did the calculator, as his name is thoughtfully printed inside on a red Dymo tape!



I love this calculator.  It works perfectly.  All the buttons are present and working.  All segments of that cherry red LED are working.  All paperwork, manuals and hardware is in superb condition.  Yeah, tatty boxes and slightly dog-eared manuals but so what?  I’m not a fan of history.  I see a lot of it as irrelevant.  Unless we’re talking tech.