We present the results of the reconstruction of the parameters of solar activity from astronomical observations in the seventeenth century. Drawings of the solar disk made by various observers differ in the observing methodology and accuracy. The distribution of the sunspot group areas from historical archives was compared with that of the modern epoch. A lack of small groups of sunspots was found in early observations. This, in turn, leads to an uncertainty in the number of sunspot groups in tens of percent. Additional uncertainty of group numbers is introduced by sorting the sunspots into groups. The latitude-time distribution of sunspots is also discussed.