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Why telephone keypads are arranged the way they are (datagenetics.com)
104 points by squeakynick on Aug 29, 2015 | hide | past | web | favorite | 46 comments

This blog post doesn’t really add anything beyond what the original paper says, though at least it links to it, though the OCR font replacement in the version he links isn’t my cup of tea. The original paper is thorough and well worth reading for anyone interested in designing keyboard-type input devices.

Here’s a link to a scan where the OCR doesn’t clobber the image http://mrserge.lv/assets/human-factors-engeneering-studies-o...

The lowest errors and fastest keying rate were actually with the standard circular telephone arrangement (most familiar), followed by the two-row five-column layout, and those were also the test subjects’ preferred layouts. In the final test between the 3x3+1 grid vs. the 5x2 grid, the vote tally was 12-3 in favor of the 5x2 gris.

I assume the company’s final choice was based on some engineer or manager’s aesthetic preferences or non-human-factors technical criteria (e.g. it fit better on a particular phone body design), though I’ve never seen any concrete explanations of how the final grid layout was chosen. Or in other words, we still don’t have a solid answer to the question “Why are the numbers on a telephone keypad arranged the way they are?”

I don't know which came first, but it might have been to make manufacturing easier give the signaling scheme keypad phones used: when you press a key, two sine waves are generated -- one represents the row and the other the column. There's two groups of 4 frequencies for 16 possible buttons; some radios have an extra column with A-D keys for the extra tones.

Some military phones used the extra keys as part of autovon.


> The Automatic Voice Network (AUTOVON) was a world-wide American military telephone system. The system was built starting in 1963,

By the way, if anyone is trying to design a number pad or calculator keyboard or similar for personal use with the goal being comfort/speed after retraining rather than prior familiarity, I’ve found it works much better to put two numbers on each finger.

Something along the lines of http://i.imgur.com/ofeQEC9.png

This is much better (faster, more comfortable, fewer errors) in my experience than the number row at the top of a keyboard, or a standard 3x3 + 1 grid calculator, computer, or phone keypad.

You also have to remember that from the beginning they knew they will also need * and # or some kind of extra keys for programming and admin tasks. With touch tone phones came many other innovations in the phone industry. So with 5x2 layout you would actually have to make it 6x2 or 5x2 +2 on the bottom. In both cases it would look and function poorly.

Also, remember that they had a lot of left over molds for rotary phone designs, and they probably intended to retrofit pay phones with rotary dials to touch tone. 3x4 layout fits a lot better into a circle than 5x2 or 6x2.

My school had us enter our IDs into a keypad to buy lunch, so I did this everyday. Then, I had to enter it in a computer and got annoyed as the system wouldn't take it. Turns out the differences was that the lunch keypad was set up like a phone with 1 on the top while computers were set up like calculators with 1 on the bottom. It had become muscle memory and I was swapping two digits because of the change in entry device. Ever since then I've thought the incompatibility baffling, as well as surprising that it doesn't cause more problems. I hadn't noticed it at all until then.

Why the difference between numeric keypads and phone keypads?

Numeric keypad layouts mimic calculator layouts, which in turn, mimicked the original ‘adding machines’. The inventors of these early devices did not perform extensive user based testing (as it often the case in technology; early adopters end up creating standards that others follow, good or bad).

The whole point of the article is the Bell labs undertook an extensive user based study to investigate which layouts might be better (Pretty much the first time this testing had been done on this issue). They tested both canonical forms of the (3x3)+1 layout and selected what we now know today as the telephone layout. (If I had to speculate as to why this layout performs slightly better than the calculator layout, I might suggest that, in the West, we read left->right and top->bottom and so this is the more natural numbering scheme).

Had extensive testing been performed by the original adding machine developers, maybe both devices would use the same layout.

Interestingly, the most creative benefit I’ve heard for keeping the calculator layout as it is, is because calculators are often used to sum up real world measurements, and these fall under to purview of Benford’s Law* Because of this, the keys which are more likely to be used as the leading digits are closer to the at-rest position of the hand and require less energy to move and press … yeah … I’m not convinced either, but it sounds good 

* http://datagenetics.com/blog/march52012/index.html

The keys near the rest position of the hand are 4, 5, and 6. The zero key is not in a particularly convenient spot for the thumb (it should be moved down and to the left), and the 1, 2, and 3 keys require relocating the index/middle/ring fingers from their home positions. The delete, space, comma, period, tab, equals, parentheses, and various operator symbol keys are mostly also inconveniently located, though the enter and plus keys are fine.

I don’t think the standard calculator numpad layout is defensible on digit or symbol frequency grounds.

Even if we want to keep the numbers in the standard place for the sake of familiarity, I would recommend adding some keys and relocating others, something like http://i.imgur.com/BnYqKLW.png

Here's a fun tidbit. DTMF supports 0123456789*# as you probably know. But it also supports A, B, C and D - not present on modern phones. These tones were added for use with remote computers and such, think today's phone menus.

The lack of them means there's a whole DTMF "column" gone. DTMF works on a grid. When you press a key, the tone for the row and the tone for the column are played simultaneously:

  (Hz) 1209  1336  1477  1633
  697 |  1  |  2  |  3  |  A  |
  770 |  4  |  5  |  6  |  B  |
  852 |  7  |  8  |  9  |  C  |
  941 |  *  |  0  |  #  |  D  |
Given the DTMF grid matches the typical layout on dialing pads, I wonder if early DTMF phones would wire the pad in the same grid to generate the corresponding tones?

There's two things I found surprising. That they tested so many circular arrangements, and that there was a measurable difference between the two 3x3+1 orientations.

If the author of the post is reading this, the image of the two vertical columns is wrong. On the site it's essentially two columns, in the paper it's five rows. That is rows 15 26 37 etc compared to 12 34 56 etc. It makes for a surprisingly large difference, at least to me. The former looks completely unusable, the latter seems quite ok :-) So maybe I should not be surprised that the two 3x3+1 setups didn't perform the same...

I'd guess that the circular patterns are all because of the norm at the time being rotary dials.

Doh! Thanks. Good catch. Yes, I made a mistake. [Fixed and updated] Thanks for letting me know.


Could be added as new design not in the paper

How curious, I had no idea american dials went from 1 to 0 with 0 the longest to dial! Where I'm from, they went from 0 to 9, with 0 being the shortest number to dial, like this:


(This is why the emergency number is 911 in the US, whereas it used to be 90000 where I'm from)

Anecdote number two is that when I was working in Denmark in 2004 or so, I noticed that all the number pads on credit card readers were calculator-style, not phone-style, which was a legacy from when Dankort was rolled out in the early 80's, just before keypad phones surpassed rotary dial phones.

(In 2010 or around there, most retailers switched their card readers to phone-style layout, so all stores had to have small signs apologizing for it, but mentioning that the rest of the world had phone-style layout, so let's just all get in line with the program...)

It wasn't only credit card readers in Denmark that used the calculator style, most of the POTS phones I've used in my life - like http://www.scandinavian-designers.com/EN/wp-content/uploads/... - have used the calculator style.

The emergency number used to be 000, but it was changed to 112 to match the rest of the EU.

Better images:


Swedish original on top, US market models on the bottom.

"The ergonomics of the handle was a focal point in the design. Additionally, the acoustic, production, and aesthetics aspects needed to be resolved. The handle was fitted in size according to the dimensions of an average face, which had been taken as the starting point of the design process."

Superior ergonomics & one of the reasons I dislike modern smart cough spy-phones. The audio is shite and software keys are no replacement for actual tactile feedback. Luckily they (rotary dial 800 series) are still available ~ http://www.vintagephones.com.au/ccp0-catshow/refurbished-tel...

NL had 0 longest to dial as well.


I believe the reason for this is so that when pulse-dialling, all the other numbers keep the correct value, i.e.:

1 = 1 pulse 2 = 2 pulses ... 0 = 10 pulses

Or else they'd all be offset by one

Kind of ignores how DTMF phones worked. The tones are actually two tones played simultaneously. Each row and column are separate tones. Laying them out in a circle could work but its not very practical.

Pretty sure DTMF came way later than pulse dialing - first keypads were just a change of interface but still pulse dialing.

If there was an early time when pushbutton phones used pulse dialing, it must have been brief. All of the pushbutton phones that I ever saw as a kid were DTMF. I'm not sure how a pushbutton pulse phone would have worked without digital electronics. This was at a time when, in the US, the phone company had a monopoly on phones, all phones were rented, and you actually paid more for "touch-tone" service.

Later on, the phone regulations were changed, and you could own a phone. That's when cheap pushbutton phones came out, that had a switch allowing you to choose between pulse and tone dialing, because you still had to pay more for touch-tone service and some regions didn't offer it.

The weird thing was, sometimes you had to use both, for instance at my college, the phone system used pulse dialing, but I had to enter a "calling card" code using tone dialing in order to call my parents and put the call on their bill.

I definitely remember (as a child in the UK) that our touch-tone phone had a pulse option that could be switched on the underside. If you flicked the switch then instead of a tone you would hear click-click-click-click when you pressed a number. This would have been in the early to mid-90s, though we were quite poor so the phone might have been older.

It took quite a long time for the UK phone system to be converted to support tone dialing everywhere so there were still places in the UK where pulse dialing was required. The last Strowger exchange, where the pulses directly stepped the switches, was only taken out of service in 1995.

There were phones out there that had a keypad but only supported pulse dialing too; if I remember correctly, my parents had one when I was a kid.

Canada was like this in the 80ies through early 90ies as well -- if it was a rotary phone, it always pulse dialed. But a bunch of the push button models had the switch so you could do either. Tonal dialing was so much quicker!

Yes, that's consistent with the US. Consumers were allowed to own their phones, sometime in the late 70s or early 80s. I got my phone with a pulse/tone switch in 1982.

Interesting! I always assumed that the keypads were introduced at the same time as touch tones. The era of keypad pulse phones must have been very brief as I'm sure I never saw one. Some early keypad phones lacked the * and # keys. Perhaps these were pulse dialed? Must research...

I have such a phone at home, we still use it every day. And it does have * and # keys, but dials the same as the older phones (the keys differ only in length of sound, not tone).

I worked as a telephone repairman in the dial era. Impatient diallers would often "push" the dial back rather than let it unwind naturally. Switch gear in the central office was sensitive to mis-timed pulses so wrong numbers often resulted. Also, as mentioned elsewhere, the early keypads sent pulses rather than DTMF, which made for an annoying clicking sound in one's ear.

I'm curious about the difference between the calculator and phone layouts.

I expect that the bias to the winning phone design came because of the bias in phone numbers - that is, because rotary dial phones would dial lower numbers more quickly, lower numbers were more sought after, and were allocated to higher population areas. This was both for personal convenience, and because it tied up the phone lines for less time with the dialing pulses.

I expect that this asymmetry also introduced a bias toward the 1-on-top dialing pattern that won, though I don't see analysis to that effect. (The original paper simply stated "that the arrangement frequently found in ten-key adding machines...was not the best [in its group]...the same geometric configuration with a different numbering scheme [one on top] was superior in keying performance... However the performance differences between the two were small".

Of course, the two arrangements primarily differ in which keys are obscured by your hand, and the proximity of the 0 key, which shouldn't be commonly used, so maybe this is just post-hoc reasoning...

Isn't there a simpler reason - a square design is easier to implement with a 3x3 matrix switch and the number layout ensures that the letters associated with the digits are in alphabetic order.

Related to this I recall reading (somewhere) about going from a keypad back to a rotary dial and how infuriating it is even though there's only a tiny difference in speed.

We humans get used to the speed as little as it is and having to go back to the old way and it's only 1/2 or even 1/10 second slower drives us crazy.

The major difference is that with a keypad you can type at your own pace, while with a dial you have to 1) wait 2) a variable amount of time for the rotary to go back in initial position for each figure. Furthermore keypads allow "muscle memory". I'm not old enough to have used extensively rotary dials but I think it's very hard to form muscle memory with rotary dials. As an aside, I don't think the difference in speed the two is "tiny".

Oh no rotary dials you got into a rhythm mostly the sound.

For medium numbers kaching ticka ticka kaching, for the first numbers 1, 2, 3 it was really quick like tick tick tick.

The zero or even 7, 8, 9 seemed to take so long compared to the other numbers.

What I wonder about is why they didn't choose the calculator layout, or, conversely, why don't calculators use phone dial layout. In both cases speed and accuracy are very important. So, why the difference.

The circular dial pads had me look up a Nokia oddity.


Note btw that it ran Series 60, meaning Symbian. Meaning that for all intents it was a smartphone.

And while not circular, Siemens also had a oddity:


And yep, that one is also running Symbian with the Series 60 UI (licensed from Nokia).

I worked in a call center where people where simultaneously using a phone and keyboard number pad accurately and not even noticing. Subtle differences between the two but still interesting.

Did the "calculator" layout yield much worse results than the winning inverted layout? If so, I'm really curious about the reasons for the difference in performance.

Should actual calculators adopt the phone layout, too? I've always been curious why not all devices use the same order (PIN entry pads, phones, calculators, etc.)

While not a complete answer to your question, American Scientist's much more detailed review of phone keypad design history says the final phone layout produced "significantly shorter keying times" than other layouts (with the exception of a layout with two five button horizontal rows that had to be rejected for other reasons) [1]. It also reports the differences between the top five contenders were statistically indistinguishable (but it doesn't record which designs were in those 5) and that the designers were aware of the calculator layouts (which were actually a lot less consistent at that time that most people assume today), so if the calculator layout had been in the top 5 it's likely they would have gone with it.

None of the calculator companies had the budgets or human factors research experience to do the kind of analysis that Bell Labs did (including some of the earliest true NUI UX research), so they just picked whatever design made the most sense to their engineers [2].

[1] http://www.americanscientist.org/libraries/documents/2005761... [2] http://www.vcalc.net/Keyboard.htm

Edit: correcting the quote to "significantly shorter" from "much shorter"

I am also curious how the calculator design came about.

There is a numberphile video about at&t's article. https://youtu.be/kCSzjExvbTQ

'We still "Hang up" when we want to terminate a call, and this refers to the action of placing the receiver back onto the hook of a phone ...'

oh my god. I'm old.

Interestingly, in German – where we mostly used phones like [1] originally, we use the word "Auflegen" (put upon) to mean the end of a call.

Different technology shapes language.

[1]: https://upload.wikimedia.org/wikipedia/commons/e/ed/Telefon0...

Telephone dial is anticlockwise, dialed clockwise.

The final winner three-by-three plus one is the only one suitable for mobile phone. Perhaps because in mobile phone screen is used as reference; in the phone keyboard the receiver used as reference. In the calculator and adding machine are not moved around and the table is used as reference.

The blog post describes a study published in 1960.

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