Jon Elson fired this volley in
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I don't believe that. It would require there be magnetic stripes
recorded on the scales at a pitch of 1 um, which is pretty close!

I don't think you understand how _multiple_ precisely-mounted read
elements in the reader head could be used to resolve dimensions much
smaller than the pole pitch -- so long as the pole pitch is uniform and
monotonic over its range.

I've done a lot of work in the past building quadrature pickups (from
scratch) and quadrature counters. If you have the precision available to
(say) mount four SETS of pickups at precisely 1/4 the "pitch" of the
"slot disk" (magnetic in this case), you get (inherently) four times the
pitch in precision. If you edge multiply the edge sensing by sinusoidal
pickup instead of square-wave choppers, you can reasonably multiply that
by 4 again without any significant loss of accuracy.

Now, take a pole pitch of .1mm (not all that fine). Multiply by (say) 10
sets of pickups at precisely measured distances between them, then do
edge multiplication x4, and you already get down to 25 microns.

I don't know how many sets of pickups there are, but 13 sets of pickups
gets it down below 1 micron. That's pretty "do-able" with current
technology.

LLoyd