As in the case of acoustic current meters, in order to determine three components of speed in a cell, the profiler is equipped with at least three transducers. A fourth can be used to track errors (see Figure 2.40). As the transducers insonify different areas, the measurement is based on the hypothesis that the current is homogeneous within the same horizontal layers. This implies that the profiler cannot be used under an angle close to the horizontal due to the risk that a large error will occur during measurement. Devices can, however, be configurated for this particular usage.