An aircraft wind tunnel model, having a pitch axis mass moment of inertia (I_yy) of 0.014 kg-m², is mounted in such a manner that it has pure pitching motion about its centre of gravity, where it is supported through a frictionless hinge. If the pitching moment (M) derivative with respect to angle of attack (α), denoted by 'M'_α, is -0.504 N-m/rad and the pitching moment (M) derivative with respect to pitch rate (q), denoted by 'M'_q, is -0.0336 N-m/(rad/s), the damping ratio of the resulting motion due to an initial disturbance in pitch angle is approximately ________ (accurate to three decimal places).