@Drewpan wrote:
I am fully aware that units matter, my point was that AutoCAD has the ability to have just "units" and the
user can select which ones. There are several settings in AutoCAD for specific units, Architecture defaults
to feet and inches for example.
@Drewpan wrote:
...but it will make no difference what the engine size is measured in.
User and the software don't care as long as the model turns out ok then it doesn't matter.
@Drewpan
You are contradicting yourself. Do units matter in design - Yes or No.
CAD History
For many years AutoCAD was unitless.
But more than a decade ago this was changed.
If you run the -dwgunits command on any AutoCAD dwg created in the last 10 years you will see that it has Document Units assigned - just like Fusion 360, just like Autodesk Inventor Professional, just like SOLIDWORKS.
The initial document units are dependent on the Template that you start with...

As long as you stay within your lane and do not communicate with others - you might never know what your Document Units really are.
Architectural is not a unit.
Imperial is not a unit.
Metric is not a unit.
These are systems that use units.
Inches, feet, yards, miles, millimeters, centimeters, meters are units in the Architectural, Imperial or Metric systems.
Here is a dialog box from Autodesk Inventor Professional when importing and AutoCAD mm units file.
(would be similar for SOLIDWORKS)

Clearly the evidence shows:
1. AutoCAD is not unitless.
2. Other CAD software recognizes that AutoCAD is not unitless (I (or you) could reproduce this and verify with any other -dwgunits setting in AutoCAD.
I have responded to countless posts on various CAD forums over the years where the issue is not knowing the Document Units of an AutoCAD file. It is easy to change the Units in any (including AutoCAD) of these CAD softwares so that there is not a conversion issue.
More history:
Years ago NASA sent a probe to Mars that crashed.
Upon investigation it was found that one contractor for the program was using metric system of units while another contractor was using imperial system of units. Because the distance to Mars is so large - the numbers were not something we would immediately recognize as "out of wack".
I see this issue frequently in FEA analysis.
Units matter. Period. Full stop.
