442 



Subsurface Geologic Methods 



mitted to a rheostat inside the oil-filled chamber by means of a flexible 

 bronze cable-and-pulley system in such a manner that the change in re- 

 sistance of the rheostat is always proportional to the change in average 

 diameter as measured by the four arms. Owing to the spring tension in 

 the arms, the tool will be approximately centered in the well, unless the 

 hole is considerably off vertical. 



The arms are held in a closed position by a steel band when going 

 in the hole. This band can be broken at will, either by firing a brass 

 projectile located underneath or by spudding on bottom. 



The chamber of the tool is filled with oil and kept hydrostatically 



Figure 206. Caliper in open position. 



Figure 207. Caliper 

 in closed position. 



