Gnevyshev–Ohl Rule on:
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The Gnevyshev–Ohl rule (GO) is an 
empirical rule
Empirical evidence for a proposition is evidence, i.e. what supports or counters this proposition, that is constituted by or accessible to sense experience or experimental procedure. Empirical evidence is of central importance to the sciences and ...
according to which the sum of Wolf’s sunspot numbers over an odd cycle exceeds that of the preceding even cycle—see the Figure. The rule breaks down under certain conditions. In particular, it invertes the sign across the Dalton minimum
The Dalton Minimum was a period of low sunspot count, representing low solar activity, named after the English meteorologist John Dalton, lasting from about 1790 to 1830 or 1796 to 1820, corresponding to the period solar cycle 4 to solar cycle ...
, but can be restored with the "lost cycle" in the end of the 18th century. The nature of the GO rule is still unclear.
References
Solar phenomena {{sun-stub