The points of volue con be indicated by means of other grophic forms such os columns or surfoces, but the fundomentol principle is the some.

9. The values on the omount scale should be continuous,- and points on the scale with their corresponding horizontol rulings should reflect the actual intervals on the scale.

10. Time should be regarded os continuous with vertical rulings used to indicate only certain intervals of time. Equol intervals of time should be indicoted by equal space intervols on the scale.

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191B 1919

Leonard P. Ayres, "The War With Germany." Government Printing Office, 1919.

Hours Spent in the Air by American Service Planes at the Front During the World War.

1. The historical labels marking three important attacks of the World War and the

Armistice give meaning to the curve.

2. Note the method of indicating the year, the month, and the day.

In this book, an illustration occupying a full page is referred to by page number. When there is more than one illustration on a page, each is identified by a letter of the alphabet. When there is more than one footnote beneath an illustration, each is numbered. Thus the cross reference 267B2 means page 267, illustration B, note 2.