The average RMSE (dot) and MAE (triangle) for a 6-month interval. The values of the three metrics are shown on the left Y-axis (black), in comparison to the average sunspot numbers (cross) on the right Y-axis (red) for the same intervals. The data for 2005–2013 (solar cycle 23) and 2017–2018 (solar cycle 24) are separated by a vertical grey dashed line. The individual metric values for each solar cycle are connected by dotted lines.