A significant advantage that weirs and flumes have over other forms of flow measurement is
exceptionally high rangeability: the ability to measure very wide ranges of flow with a modest
pressure (height) span. Another way to state this is to say that the accuracy of a weir or flume is
quite high even at low flow rates.
Earlier in this section you saw a three-image representation of liquid flow through a rectangular
weir. As fluid flow rate increased, so did the height (head) of the liquid upstream of the weir