tokens: observers (black dot, Vaquero et al. 2016 ) and additional sunspot observations by Fisher (gray triangle, Denig McVaugh 2017 ) and Hallaschka (green triangle, Carrasco et al. 2018 ). In Figure 5 , we have incorporated the sunspot group number in Derfflinger’s summary manuscript and logbooks as they are and contextualized them upon the existing sunspot group number by contemporary observers. The summary manuscript and logbooks occasionally provide observations with different group number and observations on different days. As observed in Figure 6 , based on our revised sunspot group number series, we have revised Derfflinger’s yearly sunspot group number during 1802–1824 in comparison with the number before our revision in the existing data sets (Hoyt Schatten 1998a , 1998b ; Vaquero et al. 2016 ). Our revision shows a significantly different trend of yearly Derfflinger’s sunspot group number (Figure 6 ) in comparison with that before our revision (Figure 7 ). We observed that Derfflinger’s trend is much more consistent with the sunspot number (v. 2; Clette et al. 2014 ; Clette Lefevre 2016 ) than the group sunspot number series (Svalgaard Schatten 2016 ; Usoskin et al. 2016 ) in Cycle 5. However, Derfflinger’s data are more consistent with the group sunspot number series than the sunspot number (v. 2; Clette et al. 2014 ; Clette Lefevre 2016 ) in Cycle 6. The cycle amplitude seems slightly larger in Cycle 5 than in Cycle 6. Figure 6. Derfflinger’s revised yearly sunspot group number in the summary manuscript (red diamond) and logbook (blue square) with standard errors from averaging, in comparison with the yearly number before our revision (black circle, Hoyt Schatten 1998a , 1998b ; Vaquero et al. 2016 ). Figure 7. Comparison of the yearly international sunspot number (Clette Lefevre 2016 ) divided by 20 (Muñoz-Jaramillo Vaquero 2019 ) and existing yearly sunspot group number series with backbone method (green curve, Svalgaard Schatten 2016 ; purple curve, Chatzistergos et al. 2017 ) and active day fraction method (blue curve, Usoskin et al. 2016 ). 6. Measurements of the Sunspot Positions It is difficult to determine the heliographic coordinates of the sunspots from Derfflinger’s drawings as he had not recorded an explicit time for each drawing. There are horizontal and vertical lines in the drawings, which are supposed to be parallel to the horizon and pointing to the zenith, respectively, as the manuscripts mention that the observations are made with an azimuthal quadrant. The manuscript also states that the images are upside down, i.e., the lower end of the vertical line points to the zenith. An indication of the observing time comes from the logbooks in which the sunspot drawings are inserted above, below, or within the solar elevation timings. Hence, we are using two ways of fixing the position angle of the solar disk to obtain the heliographic coordinates. The first method uses the nearest time of the solar elevation measurements to
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