GRIDS As o surface chart is rarely used for the accurate determinotion of values, few horizontal rulings ore necessary. They generally serve merely os bases of comparison. Surface charts ore generally more effective with relatively few vertical rulings. Minor time divisions can, in such coses, be indicated by means of stubs on the horizontal Kole.

COMPONENT PARTS SHOWN BY CURVES

A. Percentage Distribution of Three Types of Gasoline Feed in Engines fronn 1910 to 1918.

The total of the figures at the right-hand edge of the chart is 100%. as commented in 286.

"Automotive Induitrict," January 3, 1418. Abstracts from Time Series Charts. A Manual of Design and Construction, 1938, prepared by Committee on Standards for Graphic Presentation, under procedure of American Standards Association, with The American Society of Mechanical Engineers as sponsor body.

3. SCALE SELECTION. Since surfaces ore built up (rom the zero line or other line of relerence, the oitiount scale should never be broken. Multiple amount scales ore not opplicoble to this type of presentation.

4. SCALE DESIGNATIONS. In general, the principles ond procedures ore the some as lor line charts.

5. SURFACES Surloces should be so shoded os to present a pleasing, even tone. In stroto charts the layers should be so shoded as to be easily distinguished. The weight and spocing of the lines and dots of the shading ore important; both should be determined from a considerotion of the size of the areas to be shoded end amount of reduction intended Proiected surfaces may be indicated by lighter shoding of the some type as illustrated at the right.