Any language must be defined by a set of rules with regard to such things as sentence construction, grammar and spelling. Different languages have different rules and the rules of one language do not necessarily apply to the rules of another. Take as examples the English and German languages. In English, word order is all important. The subject always comes before the object. Thus the two sentences 'the dog bit the man' and 'the man bit the dog' mean very different things. However, in German, the subject and object are defined, not by word order but by the case of the definite or indefinite articles. Although word order is important in German, such that the sequence 'time-manner-place' is usually followed, it can be changed without any loss of meaning. The phrase'the dog bit the man' translates to: 'der Hund bisst den Mann'. The words for dog (Hund) and man (Mann) are both masculine and hence the definite article is 'der'. In this case the man being the object is shown by the change of the definite article to 'den'. Although it may seem strange, the word order can be reversed to: 'den Mann bisst der Hund' but it still means the dog bit the man. The languages are different but, because the rules are different, clear understanding is achieved. Similar principles apply in engineering drawing in that it relies on the accurate transfer of information via two-dimensional paper or a computer screen. The rules are defined by the various national and/or international standards. The standards define how the shape and form of a component can be represented on an engineering drawing and how the part can be dimensioned and toleranced for manufacture. Thus, it is of no surprise that someone once described engineering drawing as a language.
Despite the fact that there are rules defining a language, whether it be spoken or written, errors can still be made. This is because information, which exists in the brain of person number one is transferred to the brain of person number two. The first diagram in Figure 1.1 illustrates the sequence of information transfer for a spoken language. A concept exists in brain number one that has to be articulated. The concept is thus constrained by the person's knowledge and ability in that language. It is much easier for me to express myself in the English language rather than German. This is because my mother tongue is English whereas I understand enough German to get me across Germany. Thus, knowledge of how to speak a language is a form of noise that can distort communication.
The voice is transmitted through the air which in itself can cause distortions due to, for example, the ambient noise level. This is then received by the ears of the second person and transmitted to the brain. Here there is another opportunity for noise to enter the communication sequence. The game 'Chinese whispers' is based on the fun that you can have as a result of mishearing things. If there is no noise entering the communications sequence, then brain two receives the same concept that brain one wishes to transmit. However, as we all know to our cost, this is not always the case! Perhaps all the above can be summed up by a poster in New York which read, 7 know you believe you understand what you think I said, but I am not sure you realise that what you heard is not what I meant'\
The same sequence of information transfer applies to drawing (see the second diagram in Figure 1.1). In this case the brain instructs the hands to draw symbols which the receiver's eye observes and transmits to their brain. Again noise can distort the flow of information. Note that this does not depend on language and a design can be transmitted via a drawing even when the two people do not speak the same language. In the case of engineering drawing the symbols are defined by the various ISO standards which are the engineering drawing equivalent of dictionaries and grammar books.
The manner in which a designer draws an artefact can vary. One draughtsman may convey the same information using a different number of views and sections than another. This is termed 'draughtsman's licence'. It is comparable to the way a person may express a thought verbally. By the use of different words and ffiolsêl Ifids^l l^oîsêl
Brain 1 J Voice II) Air Ear ll) C Brain 2
sentences, the same concept can be presented in two or more different ways. Similarly, in engineering drawing, a design may be presented in a variety of ways, all of which can be correct and convey the information for manufacture.
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