  Rejuvenation and memory, long considered the distinguishing features of spin
glasses, have recently been proven to result from the growth of multiple length
scales. This insight, enabled by simulations on the Janus~II supercomputer, has
opened the door to a quantitative analysis. We combine numerical simulations
with comparable experiments to introduce two coefficients that quantify memory.
A third coefficient has been recently presented by Freedberg et al. We show
that these coefficients are physically equivalent by studying their temperature
and waiting-time dependence.
