190 



FARM DEVELOPMENT 



When directed to Station 13 the rodman reports the 

 measurement from the instrument down to the hub as 

 3.16 feet, making the elevation of Station 13, 107 feet. 

 So far the measurements have proven the original 

 survey correct, since upon taking the measurements 

 from the level of the instrument down to the several 

 stakes, their respective heights above datum figure out 

 the same as when measured up grade. By thus pro- 

 ceeding downward to the outlet, changing the instrument 

 once more, if there is but little variation found in any 

 of the measurements the first survey is proven accurate, 

 and when the height of datum is measured, it is found to 



Fig. 82. Same as Fig. 81, with measurements of levels taken down grade. 



be 99.99 feet above datum plane or practically correct. 

 See Figure 82. By testing the adjustment of the in- 

 strument before starting out and doing the work accu- 

 rately, the experienced man can usually depend upon his 

 levels. But if a great difference is found between the 

 two surveys, the measurements should be again made 

 with accuracy, and, if still an error appears, the instru- 

 ment should be tested and, if needing adjustment, a 

 competent person should be employed to repair and 

 adjust it. 



