Designed initially for use with a method for television band compression by variable-velocity scanning, the performance limitations of a magnetic scanner with negative feedback from a novel source are presented: also, some of the many applications of such a scanner are briefly reviewed.The justification of the presentation relies mainly on the mathematical analysis: however, measurements of current waveforms confirm that the influence of non-linearities and other factors which have been explicitly ignored in the derivation of this analysis is negligible in practice.Consideration is given to the practical application of the results, and it is shown that satisfactory operation can easily be obtained for repetitive scanning rates up to 104per second with a maximum displacement error (during a change of velocity) of no more than 0.2%.