I have a problem with an extrude I am making of a curve. The extrude I am making of the sketch is set up as follows:

Now when I Measure the sketched curves length, this value of about 115mm is very close to the mathematically derived value.

However, if I measure the two edges of the extrude that should have the same length as the sketch curve then i get the same wrong values of about 117mm for each edge:

Why the mismatch?

Hello, Mark.

I think this question is quite simple, no any mismatch here.

The difference of lenght between inner and outer edges of spiral will depends on its thickness. Outer edge will always be longer than inner edge or mid axis

hope it help.