the ratio of the per-unit change in frequency (?f)/fn (where fn is the nominal frequency) to the per-unit change in power (?P)/Pn (where Pn is the nominal active power of the rotating machine): s = (?f/fn) / (?P/Pn Found on http://www.electropedia.org/iev/iev.nsf/display?openform&ievref=603-04-08
the ratio of the per-unit change in frequency (?f)/fn (where fn is the nominal frequency) to the per-unit change in power (?P)/Pn (where Pn is the nominal active power of the rotating machine): s = (?f/fn) / (?P/Pn