-------------------------------------------
tickbox var: $sulcflag -- toggle sum normal movement
-------------------------------------------
default: 0 (FALSE)

The "SumSulc" tickbox (F3 panel, bottom right)
toggles whether or not to sum the movements of
each vertex along its normal.

When this sum is computed during area-preserving
inflation of a surface, it provides a measure of
local sulcal depth, since vertices at the fundus
of a sulcus will move further outward than
vertices on the crown of a gyrus.

This sum is saved as the "sulc" dataset during a
standard surface reconstruction.
