  For the last 20 years, the question of what are the fundamental capabilities
of quantum precision measurements has sparked a lively debate throughout the
scientific community. Typically, the ultimate limits in quantum metrology are
associated with the notion of the Heisenberg limit expressed in terms of the
physical resources used in the measurement procedure. Over the years, a variety
of different physical resources were introduced, leading to a confusion about
the meaning of the Heisenberg limit. Here, we review the mainstream definitions
of the relevant resources and introduce the universal resource count, that is,
the expectation value of the generator (above its ground state) of translations
in the parameter we wish to estimate, that applies to all measurement
strategies. This leads to the ultimate formulation of the Heisenberg limit for
quantum metrology. We prove that the new limit holds for the generators of
translations with an upper-bounded spectrum.
