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Recent work on improving and revising estimates of solar activity [Clette etal., 2014] has resulted in renewed interest in what has been called the longestrunning 'Science Experiment'. We compare four reconstructions of solar activityas reflected in the number of sunspot groups ('active regions') constructed bydifferent authors using very different methods. We concentrate on the periodsince AD 1900 where the underlying solar and geomagnetic data are plentiful andof sufficient quality and find that all four methods yield essentially the sameSunspot Group Number series. We take that as indicating that protracted andpernicious criticisms of the individual methods are neither fruitful norhelpful and we suggest that future efforts be directed towards understandingthe specific reasons why the methods give discordant results for centuriesprior to the 20th. The main area of disagreement occurs during the last 25years of the 19th century and feeds back into the time prior to that. The solarExtreme Ultraviolet flux can be reconstructed since the 1740s [Svalgaard, 2016]and with suitable scaling fits the Svalgaard & Schatten [2016] Sunspot GroupNumber series since 1865 very well, so we argue that the discordant groupseries have problems once we move out of the 20th century, and that thecommunity should concentrate on finding out what those are, so a true anduseful consensus can emerge.

Sunspot Group Numbers Since 1900 and Implications for the Long-term Record of Solar Activity