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.

In Fig. 59, an ordinary atomizer filled with writing ink was used to fill in gray areas representing night hours. If a little care is used in regulating the spray, a good uniform and light shade of gray is obtained, on top of which colored crayons will show out clearly, as, for instance, in Fig. 59 where Lighter No. 7 is represented as working on the night of September 23. To prevent the ink spreading over the chart, a strip of cardboard should be laid carefully on each edge of the surface which it is desired to ink in by means of the spray.

In making up charts like that shown in Fig. 59, the data are usually recorded on the chart day by day as reports come in. This involves a large amount of handling of the chart, and the chart is likely to be much smeared by the time the last reports are entered. If colored crayons with the color embodied in paraffin are used, very brilliant colors can be obtained, yet rubbing with the hands will not smear the colored areas. Unless a non-smearing crayon is used, it is better