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variable: $normdop -- operation along normal
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default: 0 (max)

"NormSamp, Clust Controls" parameter.  To adjust,
access pop-up by L-click on "label:" (bold).

This variable only affects the operation of:

  paint_surface
  ("val3d:" line "PAINT" button)

It currently has no effect on:

  write_label_timecourses_stats
  ("label:" line "T" and "S" buttons)

This controls the operation used when doing a
normal search:

  0 -- find max of all samples
  1 -- find avg of all samples
  2 -- find min of all samples

N.B. $normdop = 1 (avg) is incompatible with
finding uniq voxel vertices, since more than one
3D voxel will be sampled.
