  Recent work on improving and revising estimates of solar activity [Clette et
al., 2014] has resulted in renewed interest in what has been called the longest
running 'Science Experiment'. We compare four reconstructions of solar activity
as reflected in the number of sunspot groups ('active regions') constructed by
different authors using very different methods. We concentrate on the period
since AD 1900 where the underlying solar and geomagnetic data are plentiful and
of sufficient quality and find that all four methods yield essentially the same
Sunspot Group Number series. We take that as indicating that protracted and
pernicious criticisms of the individual methods are neither fruitful nor
helpful and we suggest that future efforts be directed towards understanding
the specific reasons why the methods give discordant results for centuries
prior to the 20th. The main area of disagreement occurs during the last 25
years of the 19th century and feeds back into the time prior to that. The solar
Extreme Ultraviolet flux can be reconstructed since the 1740s [Svalgaard, 2016]
and with suitable scaling fits the Svalgaard & Schatten [2016] Sunspot Group
Number series since 1865 very well, so we argue that the discordant group
series have problems once we move out of the 20th century, and that the
community should concentrate on finding out what those are, so a true and
useful consensus can emerge.
