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entry variable: $fsslope -- fieldsign near-0 valley
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default: 3000

The unlabeld entry to the left of "fs:" (variable
$fsslope), controls the steepness of additional
near-zero modulation of fieldsign saturation.

The fieldsign values (signed magnitude of cross
product of eccen and polar gradients) are small
(-0.02 to 0.02) so a steep slope is required.  To
get no truncation, set fsslope=100000.
