CONSTANT VOLTAGE 

 (D.C. Source) 



Ground Rod 



Water, 

 Level 



RECORDER 

 PEN MOTOR 



-Wi/^V- 



Vorioble Calibration Resistor 



Metal Sensing Tips 



Recorder 



Pen 



Individual Resistors Molded 

 into Epoxy Resin Wove 

 Staff Units. 



Figure 7. Practical circuit for measuring wave heights in fresh water. 



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