  Most experimental protocols for measuring scrambling require time evolution
with a Hamiltonian and with the Hamiltonian's negative counterpart (backwards
time evolution). Engineering controllable quantum many-body systems for which
such forward and backward evolution is possible is a significant experimental
challenge. Furthermore, if the system of interest is quantum-chaotic, one might
worry that any small errors in the time reversal will be rapidly amplified,
obscuring the physics of scrambling. This paper undermines this expectation: We
exhibit a renormalization protocol that extracts nearly ideal
out-of-time-ordered-correlator measurements from imperfect experimental
measurements. We analytically and numerically demonstrate the protocol's
effectiveness, up to the scrambling time, in a variety of models and for
sizable imperfections. The scheme extends to errors from decoherence by an
environment.
