How to get spline length assigned to equation variable or custom property?

I would set up something like "MyLength"="SW-Length@@@Spline1@3DSketch1@@MyConfig@MyPart.sldprt)

SolidWorks Drawings ER Blitz - Voting Results

Provide an "SW-Length" property to apply parametrically a user-selected curve (line, arc, circle, spline, or Compcurve).

Target

How to use "SW-Length@..." obtain Fig Length 484.55.

Thanks