The graphic horizontal projection of survey lines is not appre- 

 ciably affected by slight inclinations of the planchette, particularly 

 if the alidade is provided with a control bubble to secure a coin- 

 cidence of the index of the vertical arc with the nadir. 



In Fig. 24, the upper clamp, A, controls the axis in apposition 

 while leveling the planchette, and the lower clamp, B, controls 

 rotation. In setting up the table loosen both clamps. When the 

 circular level on the alidade is centered, clamp A, and when the table 

 is oriented, clamp B. Check the sights after clamping to overcome 

 possible torsional stress in the tripod legs. It is advisable, in careful 

 work, to loosen the clamping bolts of the tripod legs slightly then 

 re-clamp to secure stable conditions before completing the process 

 of orientation. 



Traverse Tripods 



Considerable is saved in both weight and expense by simplify- 

 ing the head mechanism, as in our No. 84 Traverse Tripod, and 

 mounting the same on the regular split legs commonly supplied 



