A fluid-measuring system comprising an orthogonal velocity sensor utilizing fluid pressures which can be adapted for use in flight or mobile or fixed installations. The sensor comprises a probe that is internally divided into four compartments with the longitudinal axis at right angles to the plane of orthogonal measurement, and with sensing ports oriented in proper relationship to sense the orthogonal directions of velocity moving past the sensor. By measuring pressure differences between chambers on opposite sides of the probe, and using suitable pressure instrumentation the relative airspeed in the orthogonal directions can be determined.