The chart illustrated in Fig. 8 is that for steam─shovel work on the same contract of the Construction Service Company. Line _A_ indicates the approximate number of yards moved per day. Line _B_ shows the pay─roll, ranging from $165 to $310 per day, and including a percentage for incidentals; while line _C_ represents the values of the _B_ quantity divided by the _A_ quantity, and gives the unit─cost in labor per yard for excavating and moving rock. It will be noted that the Sundays are skipped. These came on the 5th, 12th, 19th, and 26th of the month. There were some men employed on each of these Sundays; but their time was so distributed over the rest of the month as not to show for the Sundays, as the steam shovels did not work on that day. [Illustration: Fig. 7. Efficiency Chart Indicating Cost of Channeling Rock.] [Illustration: Fig. 8. Efficiency Chart Showing Costs in Connection with Steam─Shovel Work in Rock Excavation and Removal.] These charts are of a size to be filed in one of the standard loose─leaf books, and their range is from zero to about 12; thus it is possible to show any quantity to scale for any day in the month. This company has not found it of advantage to plot more than 4 lines on any one chart. Charts such as these may be marked each morning by the time─keeper upon a tracing prepared for this purpose; and at the end of the month the lines connecting the points may be inked in, and the chart blue─printed and the blue─print filed in a convenient place for immediate reference. There are several ways of working out the unit─cost from the figures, such for example as: 1. Performance per time unit 2. Performance per dollar; 3. Cost per unit of performance. The first of these is not, properly speaking, a cost statement, although it is a function of a cost statement and for certain purposes is more convenient. The number of feet of rock drilled per drill hour, is a very convenient form for record. When drilling under conditions of snow and ice, more muckers have to be employed than at other times. If the cost of mucking is included in the cost of drilling, as it frequently is, the true index of how well the drills are getting on is the number of feet per drill hour, rather than the cost of the operation to the contractor. The second method is the reciprocal of the third. Other systems will suggest themselves by virtue of the peculiar requirements of each case in practice.