Modeling with precision (m, cm, etc...)

Hello,

im doing a project that has a lot of architectural objects. Some are being imported from autocad other stuff (details) are being modelled by myself. Im having a problem that some objects that are being SCALED are not anymore having an accurate unit. If I scale an object that has 1cm, it stills have 1cm in the unit setup of the object BUT it is bigger in the scene. how can I, dont know how should I call this maybe collapse the unit so that the units still count.

Here in fact what I had as a problem. I imported a spline from corel that came very very small in the scene. I scaled it to fix in the REAL size in proportion to the other objects that I know they have the right unit setup. So I did EXTRUDE in the spline of 1 cm and the extrude became much bigger that it should be. How can I fix that or how should I proceed? Thank you for all your attention!!!  ;D

Which application?

The best application I know for precise modeling is Rhinoceros, is easy to use, and very very powerful.

www.rhino3d.com