Dimension along a curve between line intersections or points...how?

Rhino Rhino for Windows
3

Hi,
Doesnt dimOrdinate only work in straight lines, I need dimensions along the curve on the skin, like you would lay a cloth tape measure around the skin. Maybe I have underestimated what DimOrdinate can do.

25.05 though from F1-S1 to F2_S1 is an ortho view straight line dimension. the length of curve is 40.31 for F1_S1 to F1_S2

Steve