Hi Pilou,

> STL is like Polygon format or similar?

Yup, it's a polygon format.


> As there is a conversion Nurbs to polygons is there a difference between a volume in Nurbs and the result after conversion?

Yes there will be some small amount of error because of the polygon conversion. It should be pretty small though.


> Can we estimate the difference in general ? +- 0.001 Unity

It's hard to estimate it directly, it depends on various model-specific factors like how curvy the surfaces are. If you need particularly high accuracy you may want to use another CAD program to do the measurement rather than using the STL method, unless of course you were actually planning on using some STL based method for generating the physical part in the first place.

- Michael