MEASUREMENTS. 31 



DETAILS OF SURVEYING. 

 MEASUREMENTS. 



The most frequent source of error in pacing, chaining, 

 or steel taping is in counting the tallies assuming that 

 the mechanical part of the work is well done. The 

 memory should not be trusted. The only safe plan is 

 to enter each tally in the field notes as soon as that tally 

 is completed and the pins or stakes have been counted 

 by both chainmen and before the next tally is begun. 

 When timber is being estimated along the survey line 

 this error is not likely to occur, as the numbers on the 

 timber sheets are a check upon the work. 



If a pair of amateur chainmen went over some open 

 level country and reported a distance of 174.62 chains, 

 an error, if one existed, would probably be found in the 

 "tens" or tallies, and a resurvey would give 164.62 or 

 184.62 chains. The standard chain has a length of 66 

 feet. If any other unit of linear measure is used, it 

 must be made clear in the notes. 



For some classes of work steel tapes or " band chains " 

 are preferable, because, being lighter, they can be longer 

 and stretched straight er than chains. 



CONCERNING ACCURACY. 



The field work of the Forest Service extends over 

 millions of acres of wild, very rough, and frequently 

 almost inaccessible lands. In the surveying and map- 

 ping of such lands, it should be understood that the term 

 11 accuracy" does not call for the degree of precision 

 which would be applied to city lots having a value of 



