a flow - sensing probe adapted to be mounted in a conduit for indicating the flow rate of a fluid passing through the conduit . the probe has forward openings facing in the direction of fluid flow , and rear openings disposed at an angle of about one hundred and ten degrees with respect to the forward openings . pressures sensed by the forward and rear openings are used to indicate volumetric flow by using a flow coefficient that is independent of reynold &# 39 ; s number .