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Recommendation E.161
ARRANGEMENT OF FIGURES, LETTERS AND SYMBOLS ON TELEPHONES AND OTHER DEVICES THAT
CAN BE USED FOR GAINING ACCESS TO A TELEPHONE NETWORK
1 Use of figures and letters in telephone numbers
1.1 For the automatic international service, it is preferable that the
national numbering plan should not involve the use of letters (associated with
figures). The use of letters in national number plans may, however, be necessary
for national reasons. For example, countries using letters in their subscriber
numbers will naturally use them in their national numbering.
1.2 For the automatic international service to countries using letters in
telephone numbers, it would be helpful, in a country where letters are not used:
a) to include in the directory a table for converting into figures the
letter codes of exhanges in countries with which an automatic service
is available;
b) to supply, at the time of opening this automatic service, a booklet of
instructions containing the conversion table to the main subscribers to
the international service.
1.3 It would also be desirable, in countries with letters in the telephone
numbers, that subscribers with considerable international traffic should be asked
to show on their letterheads, below their national telephone number, the
international number with figures only. (See Recommendation E.123.)
2 Rotary dials (see Figure 1/E.161)
2.1 For countries which have not yet adopted any specific type of dial, the
figures on the dial should be arranged in the following order: 1, 2, 3, . . ., 0.
2.2 The dial shown in Figure 1/E.161 uses the arrangement of letters and
figures employed by some European Administrations. It may be convenient that the
dials or pushbotton sets used by international operators for semiautomatic
operating in Europe have this arrangement of letters and figures.
Note - On the North American dials and keysets, the digit 0 is not
associated with letters O and Q but with the word operator, the letter O being
associated with digit 6.
Figure 1/E.161
3 Pushbuttons or keys
3.1 10 pushbuttons
3.1.1 Arrangement and numbering
The standard arrangement and numbering for pushbuttons corresponding to
the digits 1 to 0 is as shown below:
EQ \a\co3\hs10\vs3(1,2,3,4, 5, 6,7, 8, 9, ,0, )
Extensive research has shown that this arrangement leads to shorter entry
times and lower error rates than other arrangements1.
Where a need exists within an Administration for a 2 5 array or a 5 2
array for use on special telephone apparatus, the arrays should be as shown
below:
EQ \a\co5\hs10\vs3(1,2,3,4,5,6,7,8,9,0) EQ
\a\co2\hs10\vs3(1,2,3,4,5,6,7,8,9,0)
Note - User dialling performance on these special arrays is slightly
inferior to that on the standard array given above.
In view of the fact that purely numerical numbering plans are now
recommended and that the association of letters to digits is not the same in
different countries2, it is not desirable to standardize letter symbols for
pushbuttons corresponding to each of the digits. In cases where a mixed letter-
and-digit dialling system is still in use in a country, the letters associated
with the figures in the dialling system of the country concerned may, of course,
be included on the corresponding pushbuttons of this country's telephone sets
(see Figure 2/E.161).
Figure 2/E.161
The preferred and recommended arrangement for the keys of a separate
numeric keypad on a multi-functional terminal used both for the entry of
telephone number information and data is the standard arrangement shown at the
beginning of this section.
Exceptionally, for devices intended to be used principally for data entry
but which may sometimes be used to enter telephone number information, the
1 An annotated list of literature references is available in the article cited in [1].
2 Thus, for example, on the North American dials and keysets, the digit 0 is not
associated with letter O and Q but with the word operator, the letter O being
associated with the digit 6.
arrangment whereby the first and the third row of the standard CCITT arrangement
are interchanged may be used.
Also exceptionally, telephone number information may be input from the row
of numeric keys,
1 2 3 4 5 6 7 8 9 0
of an alpha-numeric keyboard.
3.1.2 Symbols
The symbols for these buttons are the digits 1 to 0 as indicated in the
arrangements of S 3.1.1 above. These buttons are to be known as button 1, button
2, etc.
3.2 12 pushbuttons
3.2.1 Arrangement
For 12 pushbuttons the standard arrangement shown in S 3.1.1 above is
extended by two additional buttons, one to the left and the other to the right of
the button 0, thus making a pattern of four horizontal rows of three buttons each
forming a 4 3 array.
Two buttons may also be added to the 5 2 array shown in S 3.1.1 above.
These should be located below and in line with buttons 9 and 0, thus making a 6
2 array.
3.2.2 Symbols
On the 4 3 array, the symbol on the button which is immediately to the
left of the button 0 (on the 6 2 array, the corresponding button is located
below 9, and on the 2 6 array to the right of button 5) and which, according to
Recommendation Q.23, is used to transmit the frequency pair 941 Hz, should have a
shape easily identified as the general shape shown in Figure 3/E.161.
Figure 3/E.161
The symbol will be known as the star or the equivalent term in other
languages.
On the 4 3 array, the symbol on the button which is immediately to the
right of the button 0 (in the 6 2 array, the corresponding button is located
below the button 0) and which, according to Recommendation Q.23, is used to
transmit the frequency pair 941 Hz and 1477 Hz, should conform in shape to the
specifications given in Figures 4/E.161 or 5/E.161. This symbol shall consist of
four lines of equal length (b), forming two pairs of parallel lines. One pair is
horizontal while the other is vertical or inclined to the right at an angle of 80
░ as shown in Figure 5/E.161. It will be seen that two pairs of parallel lines
overlap. The ratio a/b, where a is the overlap, shall be between 0.08 and 0.18.
Figure 4-5/E.161
The preferred values are:
- in Europe3
a = 90 ░ with a/b = 0.08
- in North America2
a = 80 ░ with a/b close to the upper limit of 0.18.
The symbol will be known as the square or the most commonly used
equivalent term in other languages4.
The additional buttons with these symbols will be placed as shown below:
Standard 4 3 array
1 2 3
4 5 6
7 8 9
* 0 #
6 2 array
1 2
3 4
5 6
7 8
9 0
* #
3.3 Dual mode and engraving
Dual mode and engraving of the buttons * and # are acceptable on
3 No information is available at the present time as to which of these values would be
preferred in other continents.
4 In some countries an alternative term (e.g., "number sign") may be necessary for this
purpose, unless further investigation indicates that "square" is suitable for the
customer.
telephones and on multi-functional terminals.
3.4 Design of symbols
Symbol size and the line thickness should be appropriate to provide
optimal recognition.
3.5 Use of colours
The question of standardization of pushbutton and symbol colour for
international purposes is still not settled. In the meantime, colours different
from the digit buttons and symbols should not be used.
3.6 Position of figures, letters and symbols on push-button sets
In all push-button dials, the figures, letters and symbols should be
unambiguously associated with the corresponding buttons, preferably, if adequate
space is available, by being on the faces of the buttons themselves.
4 Additional pushbuttons for use on telephones
4.1 General
For purposes other than dialling, additional pushbuttons may be required
on a telephone. For example, a telephone may have a pushbutton to recall during
an active call, control logic (e.g., a register) or an operator, or to effect the
transfer of an active call to another station. To prevent subscriber confusion it
may be desirable that the symbols used on those pushbuttons which have identical
functions be standardized.
4.2 Specific recommendations
4.2.1 Register recall pushbutton
For the recall of a register during an active call the following methods
are possible:
- a switchhook flash,
- a depression of one of the pushbuttons of the normal 10 or 12 button
array,
- a depression of another pushbutton specially provided for this purpose
- the register recall pushbutton.
From the human factors viewpoint the depression of a pushbutton for
register recall seems to be preferable to the use of a switchhook flash.
If a special register recall pushbutton is used, this pushbutton should be
designated with the symbol R (capital) on or next to the pushbutton. The
pushbutton should be clearly distinguishable and spatially separated from the
standard 12-pushbutton array.
This symbol is recommended because:
a) it symbolizes the term "Recall" in a number of languages;
b) studies have shown that it is subject to minimal auditory and visual
confusion;
c) it avoids the difficulties inherent in specific technical terms for any
lay subscribers.
The exact position, shape and colour of the button should not be
standardized at the present time. Such standardization would inhibit design
innovation and be unnecessarily restrictive.
Note - Description of a 16-pushbutton layout has been deleted from this
Recommendation owing to lack of use of this arrangement. Reference to 16
pushbutton sets can be found in the CCITT Red Book, Fascicle II.2, Recommendation
E.161, S 3.3 and Annex A.
Reference
[1] The layout of digits on push-button telephones - a review of the
literature. TELENo. 1, 1982 (copies available at the Library of the Swedish
Telecommunication Headquarters, S-12386 FARSTA).