Hi Rudl, I'm sorry but I'm not really understanding what you are asking about... how do you mean "real size" versus x,y,z space size? Doesn't the real world have x,y,z coordinates as well?

Do you mean you need to set a unit system so you have a connection between MoI's x,y,z coordinates and a physical size? To do that you can set a unit system under Options > General > Unit system.

So for example if you want something 1 unit in width in x,y,z coordinates to correspond to 1 centimeter in physical size, set the unit system to centimeters.

- Michael