Where charts for index numbers are made on the 100 per cent basis, it would seem best to have a broad Hne for the 100 per cent line. If there is not room to extend the co-ordinate field down to the zero of the vertical scale, the co-ordinate field may be shown broken off with a wavy line at the base indicating to the reader that the bottom of the chart is not a zero line, and that the chart must be read on the 100 per cent basis.

Fig. 93 was drawn from the data of Fig. 92 as a suggestion for a type of chart which might be used where an untrained class of readers must be reached. By plotting increases above the zero line and decreases below the

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zero line, a chart is obtained which needs little space and which nevertheless is on a large scale, giving a great amount of « 2o I I ly i I I I I I 1 1 I I 1 1 I 1 1 I I I 1 1 1 1 . 1 I I I l y i I 1 1 1 1 I i ^i iin detail so as to per-