Measuring distance on a multiple planes

[Anonymous]

Hi,

My project involves projecting a decal on a three dimensional object with a curved face. I'm able to obviously measure the projected distance but I'm not sure how to meaure the actual distance along the curve. I have attached my file for referene. I'm wanting to masure the size of the eye holes where the lenses would go in particular. 

When I measure the projected distance I get about 49mm but when I measure the 3D print out I measure about 52mm. I realize that this is because of the distortion from the curved surface but how can I accurately measure this? 

Thank you 

[HughesTooling]

The only thought I have is create a plane where you want to measure.

Then use Project-Intersect an select the surface or surfaces you want to measure.

You should end up with a sketch with lines and points where they intersect the plane, then measure between points