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Point of Measurement 
The transducer must be above the maximum head P704 by at least the near 
blanking distance P107.  
For  Suppressed/  Contracted  Rectangular,  Trapezoidal  and  V-notch, 
weirs, the  head is measured upstream at a  minimum distance of 3 times 
maximum head from the weir plate to ensure the surface of the liquid is not 
affected by turbulence or drawdown. (See DRWG. 1)  
 
In the case of a Venturi flume the point of measurement should be 150 mm 
(6 inches) upstream from the beginning of the converging section and for 
a Parshall flume 2/3 the length of the converging section upstream of the 
throat section. See DRWG 2 and 3)