  The novel weak-value-amplification (WVA) scheme of precision metrology is
deeply rooted in the quantum nature of destructive interference between the
pre- and post-selection states. And, an alternative version, termed as joint
WVA (JWVA), which employs the difference-signal from the post-selection
accepted and rejected results, has been found possible to achieve even better
sensitivity (two orders of magnitude higher) under some technical limitations
(e.g. misalignment errors). In this work, after erasing the quantum coherence,
we analyze the difference-signal amplification (DSA) technique, which serves as
a classical counterpart of the JWVA, and show that similar amplification effect
can be achieved. We obtain a simple expression for the amplified signal, carry
out characterization of precision, and point out the optimal working regime. We
also discuss how to implement the post-selection of a classical mixed state.
The proposed classical DSA technique holds similar technical advantages of the
JWVA and may find interesting applications in practice.
