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An experimental method is described to measure the amplitude profiles across written tracks used in rigid and floppy disk drives. This method allows determination not only of read, write, and side-erasure widths associated with the heads, but also of the detailed shape of the written profiles. These profiles may be obtained for tracks in the as-written condition, or after modification by the write or erase functions of the head. This method was applied to floppy disk heads in order to determine the trim erase characteristics of straddle erase, tunnel erase, and the implicit side erase characteristic of the read/write core itself. A number of typical track profiles are shown, demonstrating the usefulness of this technique. It was found that the straddle erase elements exhibit erasure both under the air gap and under the poles straddling the read/write core; the tunnel erase elements exhibit uniform erasure across their erase gaps but are subject to azimuthal misalignment effects; and the read/write cores themselves exhibit an implicit erase function during normal writing which, in the case studied, extended about 360 μm (9 μm) to each side of the core. Applications of this method to evaluate heads for use at high track densities are also outlined.