170 



DEEP BOREHOLE SURVEYS AND PROBLEMS 



rotating plate with a paper sheet on which the pen 

 traces a low-pitch spiral each circuit synchronizing with 

 the pendulum swing. The pen (Fig. 109) is on the 

 jointed system consisting of an isochronous regulator 

 ensuring that the periodicity of the pen circuit is constant 

 for all positions. The trace of the grating pen is an 

 enlarged reproduction of the pendulum swinging contact 

 figure owing to the action of the electromagnet on the pen. 

 This enables the coordinate axes XX and FF to be drawn. 



The grooves of Fig. 107 form these axes by causing the 

 breaks in the circle. The coordinates of the grating center, 

 with respect to the vertical, are obtained from the diagram; 

 thus 



X = \^X 



and 



x"/k" = x'/k 



Using a coordinate length of 10 m. 



Z/10 = x/l 

 and since 



X = x"/k" . lOkC/l (lib) 



we get for a 10-m. length 



X = x"/k" . 10/cC (lie) 



