When Autodesk released AutoCAD 2007 I noticed that when I inserted a block or XREF it would sometimes scale up or down in a way I didn’t expect. After a little digging in the help file I found these system variables: INSUNITS, INSUNITSDEFSOURCE, & INSUNITSDEFTARGET.

According to the help file, INSUNITS “specifies a drawing-units value for automatic scaling of blocks, images, or xrefs inserted or attached to a drawing.” If you set INSUNITS to 0 (zero) you can use INSUNITSDEFSOURCE and INSUNITSDEFTARGET to control automatic scaling of blocks, images, or XREFs.

Values for INSUNITS, INSUNITSDEFSOURCE, & INSUNITSDEFTARGET:

For example:
I made a block that contained a single line, 1-unit long. In a blank drawing I set INSUNITS to 0, INSUNITSDEFTARGET to 1 (inches), and INSUNITSDEFSOURCE to 3 (miles). Setting INSUNITS to 0 made it an unspecified value so that INSUNITSDEFTARGET and INSUNITSDEFSOURCE would take precedence. When I inserted the block into the blank drawing, I made sure the scale was set to 1 uniformly (X, Y, & Z were all set to 1). Then I ran a DISTANCE on the line and it measured 63360 units (63360 inches = 1 mile).

When I set INSUNITSDEFTARGET to 1, I told AutoCAD that any block, image, or XREF that is inserted into the current drawing (target drawing) to be measured in inches. When I set INSUNITSDEFSOURCE to 3, I told AutoCAD to treat all blocks, images or XREFs (source drawings) that are inserted into the current drawing as if they were drawn in miles. AutoCAD then does a conversion during insertion.

NOTE: According to the help file, automatic scaling does not happen when the block is annotative.

Scenic Shop’s blog post entitled AutoCAD Imperial & Metric Conversions has some more good information on this topic. Thanks for this Matt!