Cr-Co evaporated films were written upon and read with a vibrating head apparatus. The effects of the head-to-medium spacing upon the half-pulsewidth were carefully measured between 0 and 4 μm. The formula
![P_{50} = [g^{2} + 4(d + a)^{2}]^{1/2}](/images/tex/8210.gif)
was found to hold quite well. However, the conservation of P
50after the heating of a recording and the consequent increase of

raise questions about the effect of the self-demagnetization outside the head, usually assumed as dominant.