 The objective probability of q given that the subject believes q to degree x is y. This is a curve, a function that allows reliability y to vary with the independent variable of confidence, x, with different variables used in order to allow for the possibility that the subject’s degree of belief tends not to match the objective probability, and that the level and direction of mismatch can vary with the level of confidence. The curve is specific to proposition q and to the subject whose probability function is P. A subject is calibrated on q, on this definition, if his calibration curve is the line \(x =  y\).[4]