Sunspot Number and Solar Cycle
R = K(10G + I)
R:  Sunspot Number
G:  Number of groups of Sunspots observed
I :  Number of individual Sunspots observed
K:  "Smoothing" constant.  Depends upon the power of the telescope.
Shown on the right is a detail of the last 4 of our Sun's solar cycles.  The Solar cycle displays a record of the sunspot number vs. time. Notice that two subsequent solar cycles are not well separated and uniform. The time of lowest sunspot number is not well defined, having many days with a sunspot number of 0. Often one can have sunspot groups from the old and the new cycle on the Sun at the same time.  Due to such issues with cycle date identification, the start of a new cycle is stated with an uncertainty of one or two months.