About measuring with pitot tube
The pitot static tube is mainly used for making temporary measurements of flow, although it is also used in some instances for permanent flow monitoring. It measures the local velocity of flow at a particular point within a pipe rather than the average flow velocity as measured by other types of flowmeter. This may be very useful where there is a requirement to measure local flow rates across the cross-section of a pipe in the case of non-uniform flow. Multiple pitot tubes are normally used to do this.
Their main failing is that the measurement accuracy given is normally only about ±5%, and sensitive pressure measuring devices are needed to achieve even this limited level of accuracy, as the pressure difference created is very small. More recently, measurement capabilities with the uncertainty down to ± 1% have been claimed for specially designed pitot tubes.