What Is Your Number?
iPhoneOgraphy – 27 Sep 2016 (Day 271/366)
A telephone keypad is a keypad that appears on a “Touch Tone” telephone. It was standardised when the dual-tone multi-frequency system in the new push-button telephone was introduced in the 1960s, which gradually replaced the rotary dial. The invention of the keypad is attributed to John E. Karlin, an industrial psychologist at Bell Labs. The contemporary keypad is laid out in a 4×3 grid, although the original DTMF system in the new keypad had an additional column for four now-defunct menu selector keys (see Autovon). Most keypads have a “*” key (called star or asterisk) on the bottom left and a “#” (called hash, pound, or other names) on the bottom right.
When used to dial a telephone number, pressing a single key will produce a dual-tone multi-frequency signaling pitch consisting of two simultaneous pure tone sinusoidal frequencies. The row in which the key appears determines the low frequency, and the column determines the high frequency. For example, pressing the ‘1’ key will result in a sound composed of both a 697 and a 1209 hertz (Hz) tone.
The layout of the digits is different from that commonly appearing on calculators and numeric keypads. This layout was chosen after extensive human factors testing from Bell Labs. At the time (late 1950s), mechanical calculators were not widespread, and few people had experience with them. (Indeed, calculators were only just starting to settle on a common layout; a 1955 paper says “Of the several calculating devices we have been able to look at… Two other calculators have keysets resembling [the layout that would become the most common layout…. Most other calculators have their keys reading upward in vertical rows of ten,” while a 1960 paper just five years later refers to today’s common layout as “the arrangement frequently found in ten-key adding machines”.) In any case, Bell Labs’ testing found that the layout used today, with 1-3 on the top, was slightly faster than the calculator layout with 1-3 on the bottom; however, it’s not apparent whether the two layouts were ever compared directly against each other. One advantage to the layout is that the same letter associations from rotary dial phones appears in alphabetic ordering, although it’s not clear whether this was considered as a factor in choosing the now-standard layout.
The “*” is called the “star key” or “asterisk key”. (Technically it should always have six points, as shown here, but it’s conventionally typed on computers with the plain asterisk “*”, which usually has five points in sans-serif typefaces.) “#” is called the “number sign”, “pound key”, “hash key”, hex key, “octothorpe”, “gate” or “square”, depending on one’s nationality or personal preference. (The Greek symbols alpha and omega had been planned originally.) These can be used for special functions.
When designing or selecting a new phone, publishing or using phone words, one should be aware that there have been multiple standards for the mapping of letters (characters) to numbers (keypad layouts, as with keyboard layout) on telephone keypads over the years.
The system used in Denmark was different from that used in the U.K., which was different from the U.S. and Australia. The use of alphanumeric codes for exchanges was abandoned in Europe when international direct dialling was introduced in the 1960s, because, for example, dialling VIC 8900 on a Danish telephone would result in a different number to dialling it on a British telephone. At the same time letters were no longer put on the dials of new telephones.
Letters did not re-appear on phones in Europe until the introduction of mobile phones, and the layout followed the new international standard ITU E.161/ISO9995-8. The ITU established an international standard (ITU E.161) in the mid-1990s, and that should be the layout used for any new devices. There is a standard, ETSI ES 202 130, that covers European languages and other languages used in Europe, published by the independent ETSI organization in 2003 and updated in 2007. Work describing some principles of the standard is available.
Since many newer smartphones, such as PalmPilot and BlackBerry, have full alphanumeric keyboards instead of the traditional telephone keypads, the user must execute additional steps to dial a number containing convenience letters. On certain BlackBerry devices, a user can press the Alt key, followed by the desired letter, and the device will generate the appropriate DTMF tone.