  This note introduces a simple metric for benchmarking shock-capturing
schemes. This metric is especially focused on the shock-capturing overshoots,
which may undermine the robustness of numerical simulations, as well as the
reliability of numerical results. The idea is to numerically solve the model
linear advection equation with an initial condition of a square wave
characterized with different wavenumbers. After one step of temporal evolution,
the exact numerical overshoot error can be easily determined and shown as a
function of the CFL number and the reduced wavenumber. With the overshoot error
quantified by the present metric, a number of representative shock-capturing
schemes are analyzed accordingly, and several findings including the amplitude
of overshoots non-monotonously varying with the CFL number, and the amplitude
of overshoots significantly depending on the reduced wavenumber of the square
waves (discontinuities), are newly discovered, which are not before.
