Numerical experiment indicates that the strong annual term in absolute element geomagnetic data is primarily generated by seasonal modulation of the base line: daily variations themselves do not contribute significantly. A search for an annual line using Mayaud's (1973) aa magnetic activity index, where base line control has been lost, supports the experimental results. At mid-latitudes, evidence for an annual signal in magnetic activity is equivocal; if such a signal does exist, the amplitude is at most 1 &ggr;.