on a portion of a drive population this makes individual characterization of the modal response of each individual hga important therefore what is needed is an in situ test that compares the hga modulation to an expected threshold to identify characteristic hga modulation issues during the manufacturing process and thereafter it is to those improvements and others that the embodiments of the present technology are directed referencing back to fig3 momentarily recall that the counterclockwise hga 128 rotation requires a shortening compression of the pzt 124 and a lengthening tension force on the pzt 122 external forces acting on the hga 128 in the offtrack dominant mode create the same result they compress the pzt 124 and lengthen the pzt 122 fig4 diagrammatically depicts the pzts 122 124 with their polarities swapped in relation to the longitudinal poling axis 129 the arrows 131 facing each other represent the compressive force acting on the pzt 124 and the arrows 133 facing away from each other represent the tensile force acting on the pzt 122 by the piezoelectric effect the compressive force 131 acting upon the positively poled pzt 124 produces a positive sense voltage the tensile force 133 acting upon the negatively poled pzt 122 likewise produces a positive sense voltage for purposes of this description and meaning of the appended claims when the two.