Every Rhino file has a current Unit system.
This is established when you start the new file and choose a template file.
Like SolidWorks, we always assume we are modeling at 1:1 at full scale.
The current unit system is displayed in the Status Bar at the bottom of the application window between the coordinates and current layer:
You can change the file unit system in Options > Units
If you change the unit system, Rhino will ask you about scaling. If you are modeling in Inches and you thought you were in MIllimeters, when you are asked about scaling, say No. You still want “10” to be 10.
If you knew you were modeling in inches and want to switch to millimeters, then you would say Yes to scaling so your inches are multiplied by 25.4 to be millimeters.
The dimensioning tools in Rhino also support a Alternate units. Int his case you would normally use the prefix/suffix to clearly identify the unit.