LEVELLING AND TOPOGRAPHY. 55 



The chain for measuring horizontal distances is also 

 necessary in making level results available. The 

 100-foot steel chain is perhaps the most convenient 

 and serviceable for drainage surveys. It is, however, 

 open to the objection that it is not often correct in length, 

 and hence should be compared frequently v^ith some 

 standard. The band chain should be kept on hand for 

 accurate measurements and for testing the link chain, 

 but its liability to be broken in the hands of ordinary 

 workmen, as well as the disadvantage of requiring two 

 hands for setting a pin at the fore end, makes it less 

 desirable than the link chain, from which pins are set 

 from the ends of the handles. The link chain holds 

 its place in weeds and grass better than the tape, can 

 be easily thrown across a stream, and is more conve- 

 nient for running in curves. 



Two or more flag-poles, steel pointed at one end, 

 and each bearing a flag of cloth half white and half 

 red, about 8 in. by 12 in. in size are needed for mark- 

 ing out courses for the chainmen to follow in staking 

 out the lines. 



A small hand ax for driving the stakes and a hand 

 basket for carrying them completes the outfit. A set 

 of steel marking-pins will often be found convenient. 



Taking Levels. 



In order to make the process of levelling as simple 

 as possible from beginning to end, and also keep the 

 results in the best form for use, some method of pro- 

 cedure and of keeping notes should be adopted that 

 will be general and apply to all cases that the drainage 



