  We present the so-called Sill distribution, both in the nonrelativistic and
relativistic cases, as a natural and simple way to include the effect of
threshold(s) on the energy line shapes of resonances. The Sill is correctly
normalized (even for broad states), is continuous at threshold(s), does not
require any modification to the `mass part', is easily extendable to the
multichannel case, and can be applied to both mesons and baryons. Here, as a
novel example, we employ the Sill to describe the resonance $\psi(3770)$.
