The actual equation seems to be 60f/x≅s where s is the target speed in rpm
and f is the mains frequency, solved such that x is an integer or something
else that's convenient for gearing or stroboscope disc design such as
*half* an integer.
Thus, 60*60/46=78.26 and 60*50/(77/2)=77.92.
But 60*60/48=75 and 60*50/40=75, so no discrepancy there.
On Sun, Jan 20, 2019 at 7:09 PM Michael Shoshani <[log in to unmask]>
> Whoops. Meant to include a link!
> On Sun, 20 Jan 2019 at 18:06, Michael Shoshani <[log in to unmask]
> > Kurt Nauck has a legacy page for a DOS based strobe generator, but it
> > happens to have a valuable table for calculating how many bands are
> > for a given speed reading at a particular frequency. You can also see the
> > equivalent variations between the two, with what we know as 78 being
> > at 50 Hz but 78.26 at 60 Hz.
> > Michael Shoshani
> > Chicago