Effect of varying the sunspot number (upper panels) by an increase of 30% (dashed curves) and by a decrease of 30% (dotted curves) on the evolution of the polar field (middle panels, average absolute value of the northern and southern poles) and the open flux (lower panels). The weak cycle 6 (1810.6–1823.3, left panels) and the strong cycle 19 (1954.3–1964.9, right panels) of the R_Z case are considered. The Roman numbers denote 5 time intervals which are affected by the variation of the sunspot numbers in different ways (see text).