How can you set the program units to metric?

Hello scstrange1, use the command UNITS and you will have access to a panel.
There you can set the units that you want ( in the middle of the panel).
If you set each of your files in their respective units ( inch, millimeters, meters etc... ) you will have no problems when inserting  a file into an other.
On top of the panel you will set the precision for the dimensions that you ask with the commands DISTANCE, ID etc.
The precision of the dimensions that you ask with the commands DIMLINEAR, DIMANGULAR etc... are to be set in the DDIM panel.
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Whenever you start a new drawing use a METRIC template and not the default IMPERIAL template AutoCAD is set up to use.  That template has the name acad.dwt.  An example of a METRIC template would be acadiso.dwt.If you have already started a drawing using acad.dwt use the -DWGUNITS command to reset the units for your drawing.  This is done at the command line.  Do not forget the dash ( - ) in front of the command name.