  The classical cosmological V/Vm-test is introduced and elaborated. Use of the
differential distribution p(V/Vm) of the V/Vm-variable rather than just the
mean <V/Vm> leads directly to the cosmological number density without any need
for assumptions about the cosmological evolution of the underlying (quasar)
population. Calculation of this number density n(z) from p(V/Vm) is illustrated
using the best sample that was available in 1981, when this method was
developed. This sample of 76 quasars is clearly too small for any meaningful
results. The method will be later applied to a much larger cosmological sample
to infer the cosmological number density n(z) as a function of the depth z.
Keywords: V/Vm . luminosity volume . cosmological number density . V/Vm
distribution
