The Sunspot record goes back to about 1749 and is the longest directly measured metric of the Sun that we have. If we want to compare today's activity with solar cycles of the Dalton Minimum etc we do not have any other direct method of comparison. The Layman's Count attempts to address the upward trend in recording sunspots that occurs after Wolf's death.
Wolf the inventor used the geomagnetic record of the day to establish his now famous "Wolf Count" which is the basis of today's count, but does this method attempt to align itself with the F10.7 Flux readings or record sunspots? The geomagnetic record used by Wolf is a proxy for today's F10.7 Flux values which have been recorded from about 1950. If we compare the Flux record with the sunspot there is a very close alignment even though Flux is not totally dependent on sunspot activity.
Wolf's method of recording 10 for a group and then 1 for each spot gives a much greater bias to single smaller spots. Because smaller spots and later specks are common to find in plage areas which also feed the Flux record, a check has been put in place. Plage area's are bright areas usually the result of a past region that has rotated back onto the face, these areas can be poor for producing further spots but contribute substantially to the Flux readings.
Wolf was also a fan of measuring sunspot area as a reliable guide to sunspot activity, but did he deduce that using area alone would not allow him to use the geomagnetic record as a baseline.
With so many variables in the sunspot counting method the sunspot record can be an unreliable method of recording actual sunspot activity on a daily or indeed monthly level as is observed in May 2010. An area measurement is useful as an alternative measure that can shine new light on solar activity. The DSN method is to record the total amount of pixels above the Layman's threshold (0-150 in green channel but all pixels counted) but also factor in the magnetic strength of the areas to gauge the overall solar sunspot activity. The method is to calculate the total solar darkness and multiply the result by the overall solar pixel value. It should be kept in mind that the DSN value is not a good guide to overall solar magnetic strength as plage regions are not measured.
A full description of the method is explained on the Layman's page.
The DSN graph will be updated on a monthly basis. Click on the graph for a full size view.