(dl Doited Shading (pebbled or stippled) is particularly useful for narrow layers of a stroto chart.

6. SURFACE DESIGNATION. Lobels should generally be pieced entirely within their respective surfaces If the surface is too smoH to permit this, o lobel may be placed entirely outside ond related to the surfoce by meons of on arrow. Keys should not be used if direct lobielmg is possible. However, the spoce about labeU should be reduced as much OS possible to ovo<d loo great contrast.

7. SURFACE CHART DESIGNATIONS. In general, the principles ond procedures ore the same as for line charts.

* Crosshotch ond oorolt«t line shod<ng should b« drown ot o 45 d«ore« ongi« Shoding constructed with v«rticol or horizontal lines is rtot recom* mended lo< surlocc chorts.

GRAPHIC PRESENTATION

TOTAL B T U EQUIVALENT CONSLKtO

»^^ 2» ■?« -x

PERCENT OF TOTAL B T U EQUIVALENT CONSUMED

<m 1* at 10

WPA, National Research Project, "Fuel Efficiency in Cement Manufacture," April 1938.

Total Energy Consumed in Hydraulic Cennent Manufacture by Types of Energy in the United States from 1909 to 1935.

When component parts are presented in curve charts and if space will allow, it is desirable to use two charts, one showing quantities and the other showing percentages. The above charts illustrate the reason.

Chapter 37 INDEX NUMBERS SHOWN BY CURVES

in a chart showing index numbers, 100 is used as the basis of comparison. In computing index numbers, one item or the average of several consecutive items is represented as 100. All other items are expressed as percentages of the base.