62 



ANGULAR SURVEYING 



ratio e of AiA to the stun of all the courses is called the relative 

 error of closure. Its value is 



in which 5; and Sg-, denote, respectively, the algebraic sum of 

 the latitude and of the longitude ranges and S/ is the sum of 

 all the courses. In an ordinary compass survey, e should not 

 exceed .002. 



In order that a survey may close, it is necessary and suf- 

 ficient that the algebraic sum of the latitude ranges and that 



of the longitude ranges should be equal to zero. When this is 

 not the case, the ranges having the same sign as the algebraic 

 sum must be shortened, and those of the opposite sign length- 

 ened, until this condition is fulfilled. In a compass survey, 

 the value of the correction on a longitude range is 



