OT: Vintage Calculator


Not much to do with HP calculators so I hope I'm permitted a bit of latitude on this one. I thought these pictures might be of interest to HP users too. The originals are all on Flickr from here

Tonight I powered up my first calculator again for the first time in years. It's a Sinclair Cambridge, powered by AAA batteries, with glorious red LEDs and taking about 2 seconds to calculate a cosine!


Hello Steve,

I have the Sinclair Scientific (w/o the "Cambridge"). It is very similar, except that it is RPN and scientific notation only. Yours is lightning fast when compared to mine, which takes 4 seconds to compute the cosine!




Cousin to my Radio Shack (mine is the pregnant version with a 9-volt). I sill have the one inch thick application program manual. Amazing what you could program using 30 steps. Also, amazing how inaccurate it was.

Radio Shack 4001



To say it was inaccurate is an understatement! With only 5 significant digits, mine can't even get past the second trig calculation before losing all digits in the calculator forensics test. Furthermore, it does not do any error checking for illegal operations, such as LN <=0 or ARCCOS >1 or <-1. So you can end up with a numerical result, and never realize that an error has occured.

Sinclair Scientific RPN


Edited: 10 Apr 2009, 6:00 p.m.


I happened to stumble over a danish classified add on an "Sinclair Cambridge Electronic Calculator Kit".
I don't know if it's anything special. The add is
[link: http://www.dba.dk/asp/soegning/detail.asp?annonceid=59557090]here[/link]


Edited: 10 Apr 2009, 6:12 p.m.


Hello Johnny,

Sinclair sold many of their products such as calculators both as kits for hobbyists to assemble as well as fully assembled products. It looks like they want about 88 USD for it.




I have 2 pristine programmables in the same format. The fasinating thing is the documentation that came with them.

I have a 4 volume of programs ranging from mathematics, to statistics to sciences and finance. The documentation is worth the cost of admission.

OH YEAH, they are cute too!!!!

Edited: 10 Apr 2009, 7:53 p.m.


The sinclair did not do any range reduction or checking. If you give it sensible input, it will not take ages, but the accuracy still wasn't 5 digits.

These calculators were quite cheap and were more accurate than a (normal) slide rule.

out of interest, the cambridge programmable had an undocumented feature whereby you could interrupt program execution by pressing divide. R/S would then continue.

I remember developing many fun games using this feature:


it's a pity there was not a fifth "games" library.



I LOVED that Radio Shack version! It was so cool to have a tiny little programmable. No matter that it didn't calculate things right, had precision problems, and would sometimes get caught in an endless loop -- it was still mondo cool for the day.

Sadly, I found mine about 10 years ago and it was not salvageable.

Fond memories though.



Very nice. The Sinclairs have a pretty cool form factor, if you can ignore the lack of precision. I've got the Sinclair Cambridge Programmable, which I used for some chemistry exams in high school, around 1998 or so. We weren't allowed to use a "programmable calculator" (read: TI grapher), so I brought in the Sinclair for shock value. They would have never expected such a tiny relic to be "programmable"! Not that you could write programs sophisticated enough to do any significant cheating anyway. ;)

I've still got mine kicking around, and I just put a fresh 9V in it recently to confirm it's still in working order. There's a bit of info about it here:


I remember aspiring to the programmable model but it was so far beyond my (parents) reach.

The other model that was around at the time was the Sovereign which was available in a variety of finishes, including gold, to celebrate the Queen's silver jubilee back in the 70s. Even then I knew that this model was for executives rather than engineers.


The Cambridge Scientific was my first calculator. I remember the woman in the shop trying to demonstrate it to me, but giving up because her long fingernails prevented her from pressing the keys. Later on, I swapped it with my Sister for her cassette player, which I needed as a mass storage device for my NASCOM 2.. and she threw the Cambridge away (sob).

I read that Clive Sinclair invented the LED display with built-in magnifiers. I also read that the reason for adopting RPN on some models was that he and another engineer were holed-up in a hotel room in Texas re-writing the code for the processor chip. They managed to implement a scientific calculator in the (internal) ROM space that everyone else needed for a typical 4-function machine of the day. The "sacrifice" was to use RPN instead of algebraic notation.

I was pretty happy with my Cambridge Scientific, as an alternative to 4-figure tables at school. Then my friends started appearing with nice Casio machines that had green elecro-fluorescent displays and which could:

- handle trig on angles greater than 90 degrees

- accept fractional input, and give fractional output

- accept angles in degrees/minutes/seconds

- accept key-presses without the occasional bounce

boo hoo. I did toy with another Sinclair; the Enterprise Programmable (key design faults: total absence of non-volatile storage, extremely high power consumption and therefore low battery life). I eventually migrated to Casio FX-501P which served me through school and university and is still going strong today.

thanks for the memories.



Thanks for yours, including the reference to the Nascom 2 (another forgotten name from the past). I seem to recall you could (only?) buy it in kit form.



Small red led displays with built-in magnifiers are used in the HP35 and its siblings (80, 45...); such displays were featured in HP optoelectronics leaflets and "Measurement & Instrumentation News" in 1973 (I'm recalling this from memory, excuse some lack of precision). While I admired many Sinclair products, from that tricycle car to the nice calculators to the ZX80 personal computer, I doubt such displays were his invention. But... maybe...


I bought a Sinclair ZX81 in 1971 as my first computer. As I recall it came with 1 Kb of RAM, which could be expanded to 2 Kb with an external plug-in module. It cost 250 USD, which would be over 1000 USD today. It had a horrible membrane keyboard that was almost impossible to use without missing or repeating. Attempts to save and load BASIC programs using an audio cassette tape were very unreliable. I used a black & white TV as the monitor.



The Sinclair ZX80 or 81 does not match some of your description. It cannot possibly be from 1971, as the microprocessor was yet to be invented. While its keyboard was rather basic, it was useable, and BASIC functions were associated with each key, relieving from spelling each keyword. I bought one in 1984, in the order of U$S 30-40, IIRC. I think it came with a RAM memory expansion (perhaps 16 KBy, not sure) and it was built with a very low chip count, apart of the Z80 processor. For many people here in Argentina, it was an affordable way to approach programming, as a PC costed here U$S 7000 at the time (and a professional salary was below U$S 800 per month). I have fond memories of it, but I concur it was limited.

Edited: 11 Apr 2009, 11:12 p.m.


It's usually best to add ten years to dates given by Michael. :-)

The ZX80 was indeed an early 1980's machine. I've still got one somewhere around here, purchased at a K-Mart after prices started dropping when much better alternatives appeared.

Someone actually bothered to write a version of VisiCalc for it!



The date is a typo. It was 1981, specifically October 13, 1981. The following year, the Kaypro II suitcase computer with 64 Kb and 2 5.25" floppy disk drives, that also used the Zilog Z80 CPU, came out, but I could not afford its $1595 price. I waited until 1984 when I bought a Sanyo MBC 555 PC clone with 256 Kb and 2 5.25" FDDs, and it used the NEC V20 CPU that was a functional copy of the Intel 8088 CPU used in the first IBM PC. At that point I sold the Sinclair ZX81 along with the B&W TV and audio casettes to a friend who wanted to practice Basic programming. I certainly can't criticize the Sinclair for affordability, and maybe the one you bought had a better keyboard so you have a more favorable memory of it.


Possibly Related Threads...
Thread Author Replies Views Last Post
  OT: Graphing calculator for Android ? Ivan Rancati 4 1,098 11-18-2013, 12:33 PM
Last Post: Alberto Candel
  Vintage HP 15C with bleeding LCD display Michael de Estrada 1 758 10-30-2013, 09:54 AM
Last Post: Jeff O.
  OT-The ideal calculator Matt Agajanian 0 553 09-04-2013, 01:11 AM
Last Post: Matt Agajanian
  OT: Reversing Sinclair's amazing 1974 calculator hack - half the ROM of the HP-35 Egan Ford 6 1,616 09-02-2013, 10:54 PM
Last Post: Thomas Klemm
  OT: Simulating a TI calculator with crazy 11-bit opcodes Egan Ford 8 1,579 08-13-2013, 12:06 AM
Last Post: Paul Dale
  Another non-HP RPN vintage calculator joins the collection Michael de Estrada 2 1,152 07-23-2013, 04:10 PM
Last Post: Walter B
  OT: anyone use the TI BAII Plus calculator a lot ? Gene Wright 1 677 06-15-2013, 01:08 PM
Last Post: John B. Smitherman
  OT: RPN calculator/dmm by ESI Kees van der Sanden 2 967 05-25-2013, 01:38 PM
Last Post: Kees van der Sanden
  [OT] Unknown Olivetti calculator? Cristian Arezzini 4 1,163 05-24-2013, 01:17 PM
Last Post: Thomas Klemm
  OT: The HP Calculator Cult (HCC) Geir Isene 8 1,619 02-27-2013, 04:29 PM
Last Post: Marcus von Cube, Germany

Forum Jump: