Thanks, got it

For a house that's fine but when you create furniture in SH3D that is often not precise enough.

I have not tried it, but would a 3D modeling program like Blender not be better for creating furniture?

Even with the deepest zoom level you can only move 0.1 cm with the arrow keys.

So the distance that the arrow keys move things by depends on the zoom level... is the 0.1 cm limit because you can only zoom in so far? It's hard-coded in the getMinimumScale() method. Um... if it helps you, I could make you a build with that limit removed.