My first calculator: the Litton Royal Digital 5-T

OK, kids, gather round old Gramps as he shows off the first calculator he ever owned. He got it as a present for passing his O-levels. (Actually, even if I’d had the calculator prior to taking my O-levels, I wouldn’t have been allowed to use it for the exams. Unlike math tests today, It was slide rules only in those days.) Are you gathered round? Here it is, the Litton Royal Digital 5-T from 1973.

Litton Royal Digital 5-TJust look at that beauty. It takes 4 AA batteries which last, oh, at least an hour. Fully loaded with those double-As, it weighs 9.9 oz (280g) – for comparison, an iPhone 4 weighs 4.9 oz (137g), half the weight. Dimensions? Glad you asked: 5.8" × 3.5" × 1.4" (or, for those of a metric persuasion, 147mm × 89mm × 36mm). This is one big-ass calculator.

If you look carefully you can see that it has light-emitting diodes (LEDs) for the 8-digit display, although Litton preferred to call them “Digitron Tubes”. They are the reason the batteries didn’t last. Well, that and the fact there was no auto-shutoff. If you forgot to turn the calculator off manually, the next time you used it you’d have to put in new batteries.

Another thing: there is no zero suppression for the display. Clear the calculator (the C key) and the display shows 00000000. Suppose you wanted to know what 355/113 was. Type in the 355, you’ll see 00000355. Hit the ÷ key, the display shows 355.00000. Type in 113 and you’ll see 00000113. Press equals to see what the image above shows: 3.1415929. I mean, those zeros just ooze accuracy, no?

And that K key is, er, key. It allows you to do a set of calculations with a constant. K for konstant, amirite? Let’s say I had those measurements in inches from above and I wanted to calculate the equivalents in millimeters. Since there are 25.4mm per inch, all I have to do (actually “had to do” since I used the calculator itself for this) is type 25.4 × K to set up the constant calculation, and then 5.8 =, 3.5 =, 1.4 = to calculate the millimeter equivalents. Just try and do that with your fancy-schmancy Casio.

Despite its drawbacks, I loved that calculator. Using it was like magic; a feeling I have a hard time experiencing with any other calculator. When I first got it, I’d have fun just doing calculations. I’d compare its accuracy with my slide rule. I don’t think I’ve ever got over the sheer amazement of it working and how it could be right, time after time. By the end of the 70s, I had my degree and was earning coin as a programmer and that initial sense of wonder had gone.

Album cover for It's Better to TravelNow playing:
Swing Out Sister - Blue Mood
(from It's Better to Travel)

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4 Responses

#1 Jeroen Pluimers said...
13-Jan-12 3:54 AM

Nice series on calculators.

It motivated me to find out what I had in the past (most of them were casios ) and started writing a blog article on them (and how they got me into programming).

That blog post will be in the article queue towards the end of this month. Stay tuned :)


julian m bucknall avatar
#2 julian m bucknall said...
13-Jan-12 8:59 AM

Jeroen: I look forward to it! Me, I've got a "few" more to get through and talk about...

Cheers, Julian

#3 Mike Cummings said...
23-Mar-13 10:55 AM

Today I have just picked one of these up for two quid from a second hand market. The model is identical to this and came complete in original case with instructions and the original NiCad batteries to but sadly these have leaked in the battery compartment but since I can fix most things I had a go with it and all works well. I even managed to fix the original batteries after cleaning them up and then boosting them off a car battery, This melts the crystals that lead to memory loss in NiCad batteries. They now hold a charge and will go back in to the calculator to keep it original. The LED display is in fact a vacuum tube like a radio valve. There is a date code on one of the chips and I can make out 73 so I guess this dates from that year. This firm also made typewriters and went under the name Imperial and were based in Leicester. I know have a mint example that works well and is now clean, a useful tip when plastics go dull is use a bit of Teflon spray as it fetches the shine up.

#4 wisemoth said...
23-Jul-17 3:36 AM

I've had one of these for a while - a beautiful thing. But I don't have the instructions, so I came here to find out how to use the K key! Thanks so much - you're right about it being better than the modern Casio memories :)

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