where f is the total number of spots regardless of size, g is the number of spot groups, and k normalizes the counts from different observations. Daily counts are made routinely at a number of astronomical observatories (as they have been in present form since 1848 when instituted by Rudolf Wolf at the observatory in Zurich, Switzerland) and the data are combined using the above equation and made available as daily numbers, monthly means, and yearly means. Daily numbers range from 0 to around 355, while the annual mean Wolf number varies from 0 to 10 in minimum years and from 50 to 190 for maximum years. This is also known as the Wolfer, Zurich or relative sunspot number.