System Variable for changing the measure units type from inch to mm?

When making measurements with a model/part sometimes it is necessary to
switch back and forth between "inch" and "mm". This operation requires
several key clicks. I would like to design a custom button that would
toggle between the two different types of units. However, I can't
seem to find what the name of the system variable is to accomplish
this. Any idea what the name of this variable would be for the
"measure" tool?

Thanks!

 

UNITS is the *command* to set units.

LUNITS is the system variable that covers Linear Units, and AUNITS is the
one for Angular Units. But the truth is that you can't really switch working
units in midstream without appropriately scaling your entire drawing ... for
the MEASURE command or any other.
___

 

I have a bit of kludge on my site(=.LSP)that is for people caught in the
situation of having to think of their project in both unit systems. Any time
a distance is to be entered, you type

'=

followed by the imperial distance and it forwards the metric equivalent to
acad. With a bit of work, it could be revised to work both ways.