The accuracy of the prediction of geomagnetic components for geomagnetics charts depends upon the knowledge of the various magnetic fields contributing to the secular variation (SV). If possible, the aim should be that, in the advance calculation of magnetic charts, the internal part of the SV only should be taken into account. This presumes that one can succeed in separating the internal and external portions of the SV. In this paper, it is demonstrated that the short time (that means within one sunspot cycle) secular variations of the horizontal intensityH and the declinationD at Wingst Observatory (Federal Republic of Germany) have a good correlation to the annual change of the equivalent planetary amplitudeAp, and that it is possible to vastly eliminate the activity-dependent part of the SV by assuming a linear relationship between the annual change ofAp and the external parts of the SV ofH andD.