A nonlinear transition shift (NLTS) measurement procedure for read/write heads employing a giant magnetoresistive (GMR) merged heads. The method of this invention includes the pulse-shape distortion effects on recording nonlinearity, which can significantly affect the existing theoretical formulae for calculating nonlinearity correction factor from measured partial erasure values, and second-order approximation of equation of NLTS and nonlinearity correction factor. Transition broadening effects (TBE) and partial erasure (PE) are incorporated in the NLTS measurement procedure to permit accurate isolation of the NLTS from the unrelated TBE/PE and GMR nonlinear transfer characteristic (NTC). First, a fifth harmonic elimination (5HE) test is performed at bit period T to measure a first nonlinearity value X. Then two partial erasure (PE) tests are done at two different densities, one below the PE threshold to measure a second nonlinearity value XS and the other at the same density as the 5HE test to measure a third nonlinearity value Xh. Finally, the NLTS is computed by combining the first, second and third nonlinearity values.