A displacement of a pedestrian is determined from his or her accelerations by detecting accelerations which is substantially non vertical, determining a characteristic feature in the detected accelerations correlated with a step frequency, determining the displacement on the basis of said determined characteristic.The acceleration data can be submitted to waveform analysis to determine an actualized time interval of an occurring feature, such a maximum values, from which it is determined whether the actualized time period falls within determined limit values. The currently detected characteristic feature is then determined as corresponding to a displacement step if the actualized time period falls within said determined limit value.By using non-vertical acceleration measurements, the invention can make it possible to distinguish between forward, backward, left and right stepping movements and take these into account for the navigation.