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TIME CHARTS 57

and it is then necessary to make a long sheet by pasting together several of the separate sheets. The original study from which Fig. 59 was prepared was made upon a built-up sheet seventeen inches wide and eight feet long, so that a full month of lighter operation could be shown on the one chart. ,'

In a large working chart, such as is shown in Fig. 59, very little ruling is required except for the lines limiting the width of the horizontal bar representing each lighter. In the original chart, drawing inks of different colors were used to indicate the four different conditions -- working north and working south, and idle north and idle south. Black was used to indicate towing. Solid red showed idle time in the north, and a red made up of red-ink strokes with white spaces showed idle time in the south. Thus all idle time may be indicated by red, the method of application determining whether the delay is at the north or at the south end of the trip. Working time may similarly be indicated by solid green and by green strokes with white spaces.

It is desirable in all chart work to have certain conventions by which colors would be understood to have certain definite meanings. Thus, following railroad practice, red could generally be used in chart work to indicate dangerous or unfavorable conditions, and green to indicate commended features or favorable conditions. Where neither commendation nor adverse criticism is intended, colors such as blue, yellow, brown, etc., could be used.