Hi glmr, it's not possible to represent a 100% exact helix with a NURBS curve, it has to be approximated. But it's also normal for many operations to be approximated in a similar way - things like intersections between non-analytic surfaces and sweep surfaces themselves.

But the amount of error should be very small, if what you show is causing a problem for you can you please post the .3dm model file you used to make the screenshot so I can take a look at it?

- Michael