[Perpendicular to Curve] command defines CPlane that is vertical to a select a curve.
For a point on the selected curve, the pricipal normal will be X axis of the updated CPlane. Y axis is perpendicular to X axis and the tangent at the point(binormal).
While
"Specify Curve"
prompt is displayed, select a curve.
After the curve selection is done, the preview of new CPlane will be shown.
While
"Specify a point on the curve"
is displayed, locate a point on the curve by Mouse. "Snap On Curve" mode will
be active automatically.
The updated Y axis will be dynamically shown according to the mouse cursor movement in the screen preview.