  A method is presented for measuring the integrated response in Ising spin
system without applying any perturbing field. Large-scale simulations are
performed in order to show how the method works. Very precise measurements of
the fluctuation-dissipation ratio are presented for 3 different Ising models:
the 2-dimensional ferromagnetic model, the mean-field diluted 3-spin model, and
the 3-dimensional Edwards-Anderson model.
