  We consider nonlinear, or "event-dependent", sampling, i.e. such that the
sampling instances {tk} depend on the function being sampled. The use of such
sampling in the construction of Lebesgue's integral sums is noted and discussed
as regards physical measurement and also possible nonlinearity of singular
systems. Though the limit of the sums, i.e. Lebesgue's integral, is linear with
regard to the function being integrated, these sums are nonlinear in the sense
of the sampling. A relevant method of frequency detection not using any clock,
and using the nonlinear sampling, is considered. The mathematics and the
realization arguments essentially complete each other.
