Time series of reconstructed solar activity (Φ) based on ¹⁴C (full line) and ¹⁰Be measurements (dotted line). Years are given in calendar AD years. The data points correspond to centers of the 25-year intervals. Negative values on the y-axis are artifacts and are consistent with zero within the error limits due to uncertainty in measuring ¹⁰Be and in geomagnetic field intensity.