104 



ENGINEERING FOR LAND DRAINAGE. 



To set the line, subtract the depth of the ditch at a 

 given station from the length of the gauge to be used 

 and set the line above the grade stake the amount of 

 this difference. Then the distance below the hub plus 

 the distance above it to the line equals the length of 

 gauge. This plan is illustrated in Fig. 24. 



Fig. 24. — Grading by Gauge and Line. 

 it 

 Another method of finding the point at which to set 



the line does away with all mental subtraction of fig- 

 ures and the errors which may arise from it. Take a 

 stick the length of the proposed gauge, — in the above 

 case 5 feet, — and graduate it to inches and quarter- 

 inches, beginning at the top and numbering down* 

 One-eighth inches can be obtained by estimation. To 

 use the measure at any grade peg, note the cut or 

 depth for that stake, find the same mark on the meas- 

 ure, set the bottom end of the measure upon the grade 

 peg and bring the line to this point. When the meas- 

 ure is placed upon any grade stake, the position for the 

 line is at the mark corresponding to the depth mark at 

 that stake. 



The Target Method. — Another method of grading 

 called the target plan is better for large and deep 

 ditches, and is in favor with many workmen for grad- 



