  We describe a revised collection of the number of sunspot groups from 1610 to
the present. This new collection is based on the work of Hoyt and Schatten
(Solar Phys. 179, 189, 1998). The main changes are the elimination of a
considerable number of observations during the Maunder Minimum (hereafter, MM)
and the inclusion of several long series of observations. Numerous minor
changes are also described. Moreover, we have calculated the active-day
percentage during the MM from this new collection as a reliable index of the
solar activity. Thus, the level of solar activity obtained in this work is
greater than the level obtained using the original Hoyt and Schatten data,
although it remains compatible with a grand minimum of solar activity. The new
collection is available in digital format.
