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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 
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)