Hi Michael,

>>There isn't really an offical way to mark an IGES file as having "no units".
>>And the IGES spec says that the default value for units should be value "1" which is inches.

If it's true, you ought to leave it in current way otherwise you could blame for making a can of worms (this is the IGES's nickname as labeled by Ashlar-Vellum :)

>>Do you have any other software that has a "no unit system" setting and also writes IGES files?

I thought MoI without unit system had written "none-flag". I checked Jan-18-2007 beta... I must say I was wrong...

Petr

ps:
Note that Rhino allows writting IGES with unit flags of "0" (none) or "3" (undefined). When I import it in CAM software (AlphaCAM) I get a warning for "0" flag (flag of "3" is OK):

*** Warning (IEVM_BAD_GLB_UNIT_FLAG) ***
The Unit flag (Index 14) in the IGES file's Global section is 0, which is outside the valid range of 1 to 11.
Action taken: The Unit Flag (Index 14) in the Global section has been changed to 1.

*** Warning (IEVM_BAD_GLB_UNIT_FLAG_MATCH) ***
In the IGES file's Global section, the Unit flag (Index 14), 1, and Unit string (Index 15), , specify conflicting units of measure.
Action taken: The Unit string (Index 15) in the IGES file's Global section has been changed to IN.