racteristics from those formerly exposed will also be
considered simultaneously when required, in order to arrive at best results.
2.5.1 Alphanumeric characters
As alphanumeric characters are meant the letters of a given alphabet, the numerals and the punctuation marks commonly used in editing.
Note: In all our analysis we will consider the use of the English alphabet, because of its universal diffusion around the world and its wide use in this technique.
2.5.1.1 Letters
Letters are used in this application mainly:
- in the name of each drawing to facilite to operators its identification, that is, as a title,
- in tables, list, etc. identifying items, production unities, plants, etc.,
- in legends or inscriptions to identify symbols, specific conditions of a given drawing, etc.,
- to specify physical measuring units,
- as a literal code to join succeeding drawings, - as a part of complex symbols,
- as literal codes for the identification of equal symbols, - and other uses of less importance.
Letters can be capital and lower-case. In this application,
-
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-analyzing the possible uses of letters detailed above, lower
case letters could be required possibly only to specify the physical measuring units. However, this is not worthwhile when they can be specified also, with good results, by using
capital letters. This does not involve misunderstandings or loss of information and represents a considerable simplifica
tion in the whole system.
Then, we can point out that the 26 capital letters of the English alphabet fulfil in the first instance all the requirements for texts in process control applications.
Numerals and punctuation marks are dealt with later.
The selected font must include letters which guarantee op
timal legibility. Moreover, they are required always with the same orientation and with only one size.
Discussion about the selection of the character font /which includes letters, numerals and punctuation marks/ is not included here, because in some measure it falls out of the scope of the present work. Many studies have been realized about this subject which in one form or other are published in many technical articles of the open literature^ 7,257,2583.
2.5.1.2 Numerals
Numerals are used in this application mainly;
- in consecutive numbering of the drawings,
- in tables, list, etc. indicating some data, values, etc., - to indicate the measured value of measuring instruments,
settings, etc.,
- as a part of complex symbols,
- as codes for the identification of equal symbols, - to indicate the time, if required,
- and other uses of less importance*
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-Referring to numerals, we can point out the following:
- Generally the values handled in this application do not need to have more than 6 significant figures which it is the accuracy obtained in most of the measuring instruments used in industry* However, this is not definitive.
- When they are used together with letters, they always occupy fixed places in the context, that is, preceding a physical measuring unit, following a letter in a symbol code, a name in a table or list, etc. An appropriate
convention can also be established using different colors or a discrete separation betv/een them.
- When they are used without letters, i.e. alone representing numerical values, they are written in particular places on the screen as part of a table, a drawing, etc., where they are easily identified as numbers.
- They can have always the same orientation and size.
- They could be decimal fractional /non-integer/ numbers.
In this case a reduced number of decimal places will be sufficient to express them.
- The font selected must ensure optimal legibility.
From these observations, it is evident that it is never necessary to define the character ,,0 n to differenciate the letter "0" from the numeral zero. They can be represented by the same character without possibility of ambiguity or misunderstanding.
2.5.1.3 Punctuation marks and editing symbols
The requirements for editing in this application are reduced, therefore at first glance the totality of punctuation marks commonly used in alphanumerical displays : 24,149,1501 is not necessary. Nevertheless, the use mainly of the 6-bit ASCII character code is recommended due to its frequent
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-application, its wide diffusion and general acceptance.
Additionally, some other characters and editing symbols not included into the ASCII code are proposed in order to fill some specific needs of this application.
The selection of those most useful punctuation marks is intimately related with the analysis of the physical mea
suring units and their requirements.
We have found some general characteristics to all physical measuring units which could carry us later to notable
simplifications in creating the pictures. Analyzing a re
latively high number of them, belonging to different fields of science :3lo: , we can conclude the following:
- They can be expressed always by letters of the English alphabet.
- They can be in most cases abbreviated using some letters and a reduced number of special punctuation marks or symbols.
- Their abbreviations do not need to be ended with period.
- Some units are represented universally by a letter of the Greek alphabet, but they can also be always expressed with letters of the English alphabet (ß: OHM).
- In all cases they can be written in singular number.
- They can be required always with a sole orientation and only one size.
Six-bit punctuation marks and symbols most useful in this application for editing, are tabulated in Table 2.5.1
indicating some particular uses.
-
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-Table 2.5.1
Most useful symbols and punctuation marks for editing in this application
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- in computer programming languages
- in computer programming languages
Note: In general, although it has not been particularly
emphasized, some other punctuation marks mentioned are used also in programming languages. The period, comma and semicolon symbols are not proposed to be located in the center of the cell /coincident with the vertical symmetrical axis of the cell/ because of aesthetic
reasons