How to ensure that a datum plane, or sketch - is exactly "on" a surface?

[Ank]

Imagine a solid surface calculated by some previous actions.
I wish to place a datum plane/sketch exactly on its surface. - (so that when it is extruded 2.145mm is exactly 2.145mm high in relation to the surface)
we learned that one should not attach the plane to the surface - as it creates problems.

If I now "grow" the size of the main solid - then the attached plane/sketch will be covered, and 2.145mm may become 2mm.
If I reduce the main object, a gap may be created.. resulting in multiple solids within the body.

I imagine there is a way to "pin" a datum plane or sketch to a surface, that directly translates it into coordinates? (hence not entirely depend on the attachment to some ID) - It is impractical to try to offset said datum plane/sketch by 48.234mm if needed. (hard to enter such precision)

Also: it would be useful if this "automatic" plane/sketch offsets could cause a warning if/when the main solid moved.

[Shalmeneser]

Expression in the Attachment Offset (ComboView > Data).

The DatumPlane will follow the sphere radius.

[TheMarkster]

If the datum plane is on the surface of a pad, then you can link to Pad.Length property in the attachment offset. Then if you change the length of the pad the datum plane will follow with it.

[Ank]

Thank you.