Fig. 150.
Limbs.—In the case of the limbs also it is by no means easy or practicable to take many measurements. Consequently it should be sufficient to indicate that there are a great number of different measurements for every different segment of the limbs.
There are two principal instruments needed for this: a large compass with adjustable branches, for the long segments, and a small compass for the short segments. With the large compass we measure the length of the upper arm and forearm, the length of the thigh and shin, the length of the foot. With the small compass we measure the total length of the hand, its width, the length of the fingers and of the digital segments, etc.
The circumference of the limbs is taken with the ordinary metallic tape.
In order to fulfil the present-day scope of pedagogic anthropology, it is sufficient to take only a few measurements (the form and the head), but it is necessary to take them with great accuracy, and above all, to verify one's personal ability as a measurer, so that everyone who wishes to try the experiment may have a reliable method of testing himself. To this end it is necessary to know how to calculate one's own special personal error.
The Personal Error
In anthropometry, a knowledge of the anthropometric points, the instruments to apply to them, their use and their interpretation, is not sufficient. There is need of prolonged experience in accordance with the accepted method and under a practical guide.
As a matter of fact, the degree of accuracy with which a measurement is taken is always relative, no matter who takes it, but in the case of a person who has had no practice this relativity may present so wide a margin as to be practically useless.
To obtain an approximate figure of a measurement means nothing, unless the figure is supplemented not only by a statement as to which of the accepted methods was used in taking it, but also by a minute description of the manner in which this method was carried out.