In general, sunspot cycles in the butterfly diagram overlap each other by a couple of years. The first sunspots of a new cycle appear at high latitudes during the decline of the old cycle, whereas the last sunspots of an old cycle appear near the equator during the rise of the new cycle. The boundary between cycles have been estimated by eye near the ends of solar cycles. Thus, for each cycle, sunspots at low latitudes (lower than 15) in the beginning phase should not be counted since we consider them as belongings to the previous solar cycle. Similarly, sunspots at high latitudes (higher than 25) in the declining phase are not counted since we consider them as belongings to the following solar cycle. To isolate sunspots for a given solar cycle in researches of similar purpose such a criterion is commonly adopted (e.g., Li et al., 2002; Solanki et al., 2008).