EQUIPMENT 

 ALIDADE 



407 



The alidade customarily used for this work is the triangular wooden 

 ruler, either weighted or unweighted. While a fair degree of accuracy 

 may be obtained on level ground with this type, it is unsatisfactory, be- 

 cause sights to objects above or below the level of the table are inaccurate 



Figure 1. — Light Plane-tahle ivith Camera Tripod 



or impossible, and even horizontal sights are susceptible of being inaccu- 

 rately taken unless considerable care is exercised. A simple and cheap 

 alidade was designed to replace the triangular ruler, consisting of a bar 

 of steel with the ends bent upward for arms and each arm slotted (see 

 figure 2). 



