Entering coordinates in alternate units

I would like to be able to do the coordinate entry version of
displaying alternate units in dimensions. For example, when a drawing
is specified to be in inches (well, at least blocks are considered to
be in inches when inserted), I would like to be able, for example, to
type something like 3mm on the command line, and have it interpreted
as 3/25.4" (and vice-versa, for that matter). Is there a way to do
this? (I couldn't find it in the help files or in any of the books I
looked in, which I'm hoping doesn't mean it doesn't exist, just that I
did some rotten research.

I realize Autocad wants us to believe it views coordinate units as
being dimensionless, but in reality, it is aware of how to scale
between various systems. (The units specification for block inserting,
and the above-mentioned displaying of alternate units in dimensions,
are two examples.)

-Kevin

 

An alternate way to do this, if I were working with inches and wanted
to enter a dimension in milliters, for example, would be to simply
enter it as a fraction:

10/25.4

to get the equivalent of 10 mm scaled to inches. But Autocad doesn't
seem to allow a decimal point in the denominator. Any suggestions? Is
this question so "newbie" nobody's bothered to answer, or is there
just no quick answer?

Thanks,

-Kevin