Every schoolchild knows well that on every calculator and number pad of the keyboard, the row of numbers always starts from the bottom. This applies to both plastic and virtual ones, which are part of all home computers and mobile phones.
But who among you realizes at first glance that on the dial of your telephone it is exactly the opposite and the values grow downwards?
This peculiar contradiction was recently recalled by a series of tweets that rechristened it the one of the biggest design disasters of all time. But such a judgment is unnecessarily harsh and partly meaningless, because both directions of the user interface have their historical and statistical justification. Today we’ll show you what’s behind it.
Benford’s law
Table of Contents
If the age of the design was the sole deciding factor, calculators would of course have the correct ranking. Their user interface is based on the adding machines of the turn of the 19th and 20th centuries.
A nice example is the L-160 mechanical model from the Monroe Systems for Business stable pictured below.
Monroe L-160 adding machine from the first half of the 20th century
His number lines really start from the bottom, so lower values are closer to the accountant’s fingers. It has its own logic. Zero is (not only) one of the most important values due to rounding, and the statistical probability of the others gradually decreases with their gradual growth.
We even have a mathematical law for this – we call it Benford’s – according to which “in many natural data sets, numbers begin with the digit 1 far more often than any other digit.” The number 9 is at the tail end, so it was at the very end of the adding machines.
Relative frequency of occurrence (%) of each digit (k) according to Benford’s law
The same layout has already been adopted by modern calculators, including the software ones on our mobile phones, due to experience.
It should be noted that, especially when holding the phone with one hand, the ergonomics change somewhat and the upper row of digits is much more accessible to the thumb than the lower rows. Tapping zero can be a real pain with longer fingers.
Okay, but why didn’t the first push-button telephones adopt the same practice? Engineers from the Bell System company are responsible for everything, which introduced the first telephones with tone dialing (DTMF) in the USA in the early 1960s.
Dialing a telephone number based on the DTMF principle works roughly in such a way that each digit creates a beep in the electrical network consisting of a pair of different frequencies and a short delay, which is recognized by the control panel.
Table of DTMF two-tones for each of the digits/characters (digits):
| 1209 Hz | 1336 Hz | 1477 Hz | 1633 Hz | |
|---|---|---|---|---|
| 697 Hz | 1 | 2 | 3 | A |
| 770 Hz | 4 | 5 | 6 | B |
| 852 Hz | 7 | 8 | 9 | C |
| 941 Hz | * | 0 | # | D |
Example: Press digit 5 = The phone will produce a short compound tone consisting of a high and a low frequency component of 1336 Hz + 770 Hz. The tone later settled to a minimum length of 50-100 ms with a pause of at least 20-50 ms.
Interesting fact: Why doesn’t a digit have only one frequency? Each of these two tones can be more easily filtered and separated from the noise – it has a unique signature. The switchboard captured both the low and high frequency components in the incoming signal and, when they matched, recognized much more reliably that it was really the number 5 and not a mistake caused by noise, human voice, etc.
All in all, dialing the entire phone number in tone dialing was suddenly much faster than in the original pulse dialing, in which, on the other hand, each digit is created by a different length of interrupted sequence of electrical pulses, which is generated by a rotary dial returning to the starting position.
At Bell Labs, they were experimenting with a bunch of new dials for DTMF. Once the buttons imitated the original rotary arrangement, the second time they tried a rather long row like on an English keyboard, and the third time finally a matrix with the same order as on adding machines.
2500 DMG black 1980 AT&T Push Button Telephone (1980s)
However, the engineers ran into a bunch of ergonomic obstacles during testing. Those familiar with accounting calculators pressed the buttons too quickly, the sequence of tones blended together – there must be a minimum time gap between them – and the switchboards failed to recognize it.
And the common people wanted to read the dial like a novel
At the same time, telephones already used letters for memory codes (for example, 2-ABC) and reading from left to right and top to bottom was understandably much more natural for Americans.
Therefore, a layout that prefers natural text reading habits (at least in our cultural circle), unlike accounting calculators, eventually won out in A/B tests, and this practice was then adopted by other manufacturers.
Phone dials and calculators on the Google Pixel phone
A different style has persisted to the present day, which is why phone programs and calculators have staggered top and bottom lines. The only thing they usually agree on is the zero symbol as a special value in many ways. She is practically always down.
