Page 75 



CONTROL AND SIGNAL BUILDING 



223 



Table 3. — Requirements for triangulation and traverse 

 TRIANGULATION 



First order 



Second order 



Third order 



Strength of figures: 



Desirable limit, XR\ between bases 



Maximum limit, 2i?i between bases 



Desirable limit, Ri, single figure- _-_ 



Maximum limit, R\, single figure. ^ 



Discrepancy between computed length and measured length of base 

 or adjusted length of check line, not to exceed. _ 



Triangle closure: 



Average, not to exceed 



Maximum, not to exceed __. 



Usual number of observations: 



Positions with 1-second direction theodolite. _ _ _ 



Positions with 2-seeond direction theodolite 



Sets with 10-second repeating theodolite _ . 



Rejection limits: 



Direction theodolite, 9- or 6'/^-inch _ 



Horizon closure: 



With 10-second repeating theodolite-. _ 



Base measurement: 



Actual error of base not to exceed 



Probable error of base not to exceed _. 



Discrepancy between 2 measures of a section, not to exceed 



Astronomic azimuth , probable error of result 



80.. 

 110. 

 15.. 

 25.- 



100. 

 130. 

 25. _ 

 40.. 



1 in 25,000- 



1 in 10,000 



1 sec. 

 3 sec. 



3 sec- 

 5 sec. 



16... 

 24...- 

 5 to6- 



12.,.. 

 2 to 3. 



1 in 300,000-.. 

 1 in 1,000,000. 

 10 mm V^" -- 

 0.3 sec'. 



5 sec 



1 sec. per angle. 



1 in 150,000. 

 1 in 500,000_ 

 20 mm VA- 

 0.3 sec • 



125. 

 175. 

 25. 

 50. 



1 in 5,000. 



5 sec. 

 10 sec. 



4. 

 4. 

 1 to2. 



5 sec. 



IH sec. per angle. 



1 in 75,000. 

 1 in 250,000. 

 25 mm V':- 



TRAVERSE 



Closing error in position, not to exceed . ._ 



Probable error of main scheme angles . . . 



Number of stations between nstronomie azimuths ... 



Astronomic azimuth, discrepancy per main-angle station, not to 



exceed _ 



Astronomic azimuth, probable error of result 



1 in 25,000 



1.5 sec 



10 to 15-..- 



1 .0 sec 



0.5 sec 



1 in 10,000 

 3.0 sec... 

 15 to 25... 



2.0 sec... 

 2.0 sec... 



1 in 5,000. 

 6.0 sec. 

 20 to 35. 



5.0 sec. 

 5.0 sec. 



CIRCLE SETTINGS 

 Initial settings for 10-second repeating theodolite 



Initial settings for 2-micrometer theodolite 

 Two Positions of Circle Four Positions of Circle 



Six Positions of Circle 



Eight Positions of Circle 



*Although only 8 positions are here specified, the practice of the Coast and Geodetic Survey is to use 16 positions. Very little addi- 

 tional time is required. The average triangle closure is decreased in this way from 3 seconds to about 1 V2 seconds. 



' This is the requirement for a Laplace azimuth. In the recent practice of the Coast and Geodetic Survey the only azimuths ob- 

 served are Laplace azimuths. 



