  We have investigated high-precision measurements, beyond the standard quantum
limit, utilizing non-classical states. Although entanglement has been
considered a resource for achieving the Heisenberg limit in measurements, we
show that any advantage expected from using entanglement is dependent on the
measurement in question. We investigate several measurement scenarios and
illustrate the role of entanglement as a resource for quantum high-precision
measurement. In particular, we demonstrate that there is a regime wherein
entanglement not only does not help, but prevents the achievement of the
fundamental limit.
