Sometimes you may need to find one of the many files that make up AutoCAD. If the file is in the AutoCAD support file search path, you can use the (findfile) AutoLISP function to track it down. At the command line, type:
(findfile “filename.ext”)
where filename.ext is the exact file name and file extension.

Caption: Example: Using (findfile) at command line to find location of acad2008.lsp file.

Your support file search path is defined in the File tab of the Options dialog box, accessible through the Tools menu. Press the Add button to include additional locations in the search path.

Caption: Set the Support File Search Path in the Files tab of the Options dialog box.

In AutoCAD, true ellipse objects do not have a thickness or width.

Caption: An AutoCAD Ellipse object has no thickness or width.
If you want to assign a thickness or width to an ellipse, you need to create a 2D polyline version of the ellipse. Set the PELLIPSE system variable to 1 (one). Do this by typing PELLIPSE at the command line, then typing 1 when prompted to enter new value. When PELLIPSE is set to 1, any ellipse you draw using the Ellipse command will be a 2D polyline approximation.

Caption: 2D polyline approximation of an ellipse provides options for thickness.

If you have existing ellipses to convert to 2D polylines, you can export the ellipses to DWF format, then reinsert into the drawing. First, set the PELLIPSE system variable to 1 and the PLINETYPE system variable to 0 (so polylines aren’t changed when they are placed in the drawing). Type Dxfout at the command line. In the Save As Type pull-down list, select AutoCAD R12/LT2 DXF (*.dxf). Go to the Tools menu in the Save Drawing As dialog box and select Options.

Caption: Select AutoCAD R12 DXF in the Files of Type pull-down list, then select Options from the Tools menu.

On the DXF Options tab, check the Select Objects box.

Captions: DXF Save As options. Check the Select Objects box to pick individual ellipses to save as DXF.

Click on Save, then select your ellipses. Press Enter when you’re done. Type Erase at the command line, select the ellipses, and press Enter to erase them. Type Ddinsert at the command line, then select your DXF file. Make sure the Specify On-screen to Insert the Block box is not checked. Select the Explode option, then click on OK.

Caption: Ddinsert dialog box.

You can edit your dimension styles to set the text color of tolerances to be different than the dimension text.

Caption: Highlight dimension tolerances by making them a different color.

By default, AutoCAD gives dimension tolerances the same color as the dimension text. To change the color of the tolerance text, enter Ddim at the command line. This launches the Dimensions Style Manager dialog box. Select the dimension style you want to change, click on Modify, then click on the Primary Units tab. In the Suffix field, type:

\Cxx;

where xx is the ACI (AutoCAD Color Index) number of your desired color. Note that the C must be uppercase.

Caption: Indicate your desired tolerance color for a particular dimension style in the Suffix window of the Primary Units tab.

If you receive the following message when you are creating associative dimensions (DIMASSOC system variable set to 2), you are probably trying to dimension an object that does not support associative dimensions.
Specify second extension line origin: end of Non-associative dimension created. 
These objects include:

1. All dimensions
2. Leaders
3. Tolerances
4. Multilines
5. Any block inserted using the Minsert command
6. Viewports
7. Hatches
8. Mirrored or nonuniformly scaled block references
9. Images
10. Trades
11. Most 3D objects, including solids, 3D faces, polygon meshes and mesh vertices, polyline meshes and mesh vertices, and 3D face records
12. Custom objects that do not implement the AcDbDimProtocol for supporting associativity