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Nonlinear response in magnetostrictive sensors significantly affects the spin-stand parametric measurements used to characterize writer and reader performance of recording heads. A simple production level test defined as the nonlinear distortion (NLD) ratio was used to quantify the degree of reader nonlinearity. A positive NLD value represents the presence of reader distortion while a value of zero represents no distortion. On a large population of heads tested, the median NLD value was 0.25, which is equivalent to an amplitude loss of 10% for an isolated pulse due to reader saturation. A detailed analysis of the measured data on nonlinear transition shift, partial erasure, and PW50 of these production heads show that greater than 50% of the measured variance is due to readback nonlinear distortion rather than true performance variation of the device.