When several spacecraft pass at different distances from a localized structure like a field-aligned current tube, the corresponding magnetic signatures recorded on each spacecraft generally show different timescales, due to the different viewpoints of the spacecraft. For this reason, it is impossible to identify the presence of a unique structure from these signatures by using the classical correlation functions. In this paper, we present an adaptive correlation function which is a new analysis tool allowing to look for such correlations whatever the dilation factor is between two signals. ¿ 1998 American Geophysical Union