CHAP. IV.] FALSE STATION 91 



theodolite to the true station as a " distance," enter the 

 traverse table, and take out the greater increment if lies 

 between 45° and 135°, or between 225° and 315°, and the 

 lesser increment for other angles. The accompanying diagram 

 (Fig. 12) will assist the memory. Refer this increment to the 



Fig. 12. 



" table of subtended angles by various lengths at different 

 distances " (using the distance of the object observed), and 

 find the corresponding correction in arc, which mark + or — 

 according as () is under or over 180°. Apply this correction to 

 the observed theodohte angle. A " table of subtended angles " 

 IS unnecessary if the formula 



number of feet subtended x 34 



Angle m seconds = — — 



distance of object m sea miles 



be used instead. 



The angle to the zero must be corrected in the same manner 

 as other angles ; the correction to zero mil be nil if the angle 

 to the true A reads 180° or 360°. 



The sign of the correction to the true station will be reversed 

 when correcting angles taken to the false station at one of the 

 other stations, but will be the same in amount. 



The use of the foregoing method is facihtated by placing 

 the false A in such a position that the theodolite reading of 

 the true A is not large. 



A simple and effective way of reducing the angles to the Two False 

 true A is to measure the angles taken to the same object from on Oppo- 

 two positions at equal distances on either side of the true A , ^j^^j^^*^®^ 

 the Une joining the two positions passing through the true A. True A 



