What happens when your trusty calculator fails?

March 2026

History

School days had seen me using Log Tables, which apart from other magic could simplify long multiplication. Unlike many of my school friends I enjoyed this, although care had to be taken to ensure log and antilog tables were not confused.

Later on, slide rules were used - my model is a British Thornton P271. Slide rules are capable of a wide variety of mathematical functions at great accuracy - they were used on the Apollo moon landing mission for such calculations as rocket trajectories and fuel loads, and Buzz Aldrin reportedly took his to the Moon on Apollo 11.

Another mechanical device we used around this time was the pinwheel calculator, like the one illustrated. This used a combination of levers and rotating drums for basic addition, subtraction, multiplication, and division. These were simple to use, but not sufficiently powerful to warrant a trip to the moon.

Pocket calculators

I don't know when I acquired my pocket calculator, possibly the 1980s.

In 1976 Sharp released the EL-8026, the world's first calculator using photovoltaic cells. This was improved in 1979 by the use of a new ultra violet cell that could be powered by fluorescent lights. Sharp subsequently produced a range of solar-powered, wallet-type calculators in the early 1980s, of which my EL-344A is an example.

I later acquired my Dad's Casio scientific fx-361 calculator. Its wallet still contains the original Argos receipt, now illegible. Dad had inked over the fading figures, showing that he bought if for £12.95 on 11 August 1986.

Unlike mine it is battery powered, using two LR44 batteries said to provide 720 hours of use. Fortunately it has an automatic power-off, as it's easy to forget to switch it off when you're used to solar-powered models.

The instructions state that the batteries should be removed after an extended lack of use (how long is that? ) and replaced in any case after 2 years. Well that hasn't happened.

So Dad's old calculator still works well, but mine has a few hiccups.

The first problem is that the device fails to charge and the display stays blank. This particular variant has no battery cell (unlike the 344R and 344W variants with their 1½ V cells). It stores charge in a capacitor for a short period, but needs to be exposed to sunlight, be within 2½ m of a 100W bulb or 1½ m of a 15W bulb.

With nothing to lose, I remove the back case, dismantle the contents and look for any damage or dust. Having found no problem the device is reassembled, and rather strangely it now works perfectly.

The second problem arises a year later, in 2026, when the '5' key fails to register - all other keys display perfectly and consistently. Time to schedule another disassembly.

There are 8 cross head screws in the back panel - these are all the same size and all need to be removed. The back can then be prised away.

Exposing the innards displays a surprisingly simple layout - the key sensor panels, a flexible circuit board with chip and the capacitor. The solar cells are obscured by a white plastic cross-piece.

Pleasingly, all components are mounted on pegs - there are no screwed, glued or soldered joints to complicate disassembly. The thin circuit wafer is first removed, allowing the button sensor sheets to be removed and the keyboard membrane exposed.

I was expecting to find either a build-up of dust or degraded sensor surfaces, but all seemed in good shape.

My attempted repair of our TV remote previously had found degraded conductive surfaces on many buttons - apparently poor manufacturing had caused silicone oil to gradually weep out of the keypad over time. Despite cleaning these and refreshing the conductive coat the remote proved to be beyond repair.

This was not the issue with the pocket calculator, as the keys do not appear to have conductive surfaces but instead depress the sensor contacts.

Having found no obvious problems I cleaned and replaced each component and replaced the back.

Switching back on, as before, the problem had magically disappeared.

While this is a satisfactory outcome, it would have been better to have identified a specific problem, as one of those buttons may well fail again in future …

Addendum

It's April 1st 2026, and time to watch the Orion spacecraft launch on the Artemis II mission to send 4 astronauts on a lunar flyby.

The last moon launch I watched was in 1969 when the Saturn V rocket of Apollo 11 lifted off with Neil Armstrong, Michael Collins and Buzz Aldrin.

Todays adventurers took mobile phones to photograph Earth and her moon. Technology advances apace - slide rules and pocket calculators have had their day!