Kent Elrod sent this AutoCAD tip that is mostly for civil project designers.
“If you have changed the direction of North using the units or northdirection variable and you then want to draw a line 90° in the World Coordinate System, here’s how. After starting the line command and picking a point, enter this at the command line: @12’<<90. Note that there are two << instead of the usual one. This method will overwrite the snapang setting as well. I found that one looking through an old 1988 Release 10 AutoCAD reference manual.”
Notes from Cadalyst tip reviewer R.K. McSwain: This may be a seldom used tip for most people, but knowing this one and using it could save a lot of frustration. You are more likely to need this tip if you frequently deal with drawings from others.