This paper considers the problem of control-oriented errors quantification for a known linear discrete-time SISO model under coprime factor perturbations and measurement disturbance. Upper bounds on exogenous disturbance, measurement disturbance and perturbations in output and control are assumed to be unknown to the controller designer. The problem under consideration is to compute data-consistent upper bounds on steady-state tracking errors in the framework of the lscr₁ robust control theory.