@samuel_t said:

Maybe if I ask user for a height in mm instead of cm, size of imported model will be more accurate...

I would prefer it, either as default or at least as option.

1. Can you explain, how size of imported object is calculated? I am not able to import objects in correct size. See attached example - block 10x20x30mm
   
   It was exported to STL, and imported back by Universal Importer.
   Height set to 1 cm
   
   no texture, no reduction.
   Result :
   

I do not know, what I am doing bad....

2. I am using milimetres as default in Sketchup - if the sizing rules would work, can it be changed into mm instaed of cm?