  Structural disturbances, such as galaxy mergers or instabilities, are key
candidates for driving galaxy evolution, so it is important to detect and
quantify galaxies hosting these disturbances spanning a range of masses,
environments, and cosmic times. Traditionally, this is done by quantifying the
asymmetry of a galaxy as part of the concentration-asymmetry-smoothness system,
$A_{\rm{CAS}}$, and selecting galaxies above a certain threshold as merger
candidates. However, in this work, we show that $A_{\rm{CAS}}$, is extremely
dependent on imaging properties -- both resolution and depth -- and thus
defining a single $A_{\rm{CAS}}$ threshold is impossible. We analyze an
alternative root-mean-squared asymmetry, $A_{\rm{RMS}}$, and show that it is
independent of noise down to the average SNR per pixel of 1. However, both
metrics depend on the resolution. We argue that asymmetry is, by design, always
a scale-dependent measurement, and it is essential to define an asymmetry at a
given physical resolution, where the limit should be defined by the size of the
smallest features one wishes to detect. We measure asymmetry of a set of
$z\approx0.1$ galaxies observed with HST, HSC, and SDSS, and show that after
matching the resolution of all images to 200 pc, we are able to obtain
consistent $A_{\rm{RMS, 200pc}}$ measurements with all three instruments
despite the vast differences in the original resolution or depth. We recommend
that future studies use $A_{\rm{RMS, x pc}}$ measurement when evaluating
asymmetry, where $x$ is defined by the physical size of the features of
interest, and is kept consistent across the dataset, especially when the
redshift or image properties of galaxies in the dataset vary.
