When I compare the outcome of

`_Sphere 0 10 _EnterEnd`

with

`_SubdSphere 0 10 _EnterEnd`

I expected to get two spheres of radius 10. Instead, the SubD sphere has the radius of about 8.3.

When I compare the outcome of

`_Sphere 0 10 _EnterEnd`

with

`_SubdSphere 0 10 _EnterEnd`

I expected to get two spheres of radius 10. Instead, the SubD sphere has the radius of about 8.3.

The vertices of the flat SubD are lie on the sphere with the specified radius.

The more subdivisions, the closer the fit of the smooth SubD with a NURBS sphere.

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I see that, thanks - itâ€™s just that the result is unexpected, and it precludes precision modeling with SubD.

SubD isnâ€™t really intended for precision modellingâ€¦

For instance you canâ€™t achieve perfect circles.

As @martinsiegrist already alluded to the measurements you give to such commands work on the control network.

Itâ€™s just differentâ€¦

When I need a precise fit for something cylindrical, I usually subtract a NURBS cylinder.

That should get fixed in Rhino 8 SR3:

https://mcneel.myjetbrains.com/youtrack/issue/RH-75649/SubDSphere-wrong-radius

SubDs might not be able to represent exact circles, but you can still get precise and controlled positions of the limit surface vertices.

RH-79066 is fixed in Rhino 8 Service Release 4 Release Candidate

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