SEISMIC METHODS 



749 



Z = 



a 



(--0= 



D + R 



is included on the right hand side of the plotting template so that reflec- 

 tions from very gently dipping interfaces may be plotted with the D-scale 

 set on zero. The D-scale and the plotting template are easily detachable, 

 and a separate set of these items must be made for each velocity-depth 

 function used. 



Fig. 455. — Graphical analogue computer for plotting of reflection data in 

 vertical section, given only the corrected reflection time T and the move-out 

 time t. 



On the plotting table shown in Figure 455, the two paper finger clamps 

 at the top of the table are operated by electrical solenoids attached to the 

 back of the table. They are released by a foot-operated switch, leaving 

 the operator's hands free to slide the profile paper along, and to line the 

 pivot point upon a new shot-point. The two troughs on the sides of the 

 table hold long rolls of profile paper. During the operation of the plotting 

 machine the paper is rolled from one trough across the table to the other. 



The D-scale ways are driven by a small reversible electric motor located 

 on the under side of the table. This feature allows the scale to be rapidly 

 and accurately set in the desired position for the pivot about which the 

 template swings. 



It is worth noting that the plotting system described here can be made 

 to approximate closely many of the velocity-depth functions derived from 



