Figure 4.—Position of disk in slot in plastic shelf. Visible at the back of the shelf is the zero-adjust resistor, Ra, which is 
adjustable through a hole in the end of the case. Note also (1) the chordal hole through the axle, visible from the end of the 
axle used for attaching the weight cord, and (2) the phonowire connections to the slidewire. 
Figure 5.—Slidewire contact whose pressure is adjustable from outside the plastic case. 
