Developing Drawing Strategies: Part 1 - AutoCAD 2011 and AutoCAD LT 2011: No Experience Required - page 123

Select object to offset or
Pick this line
to offset.
FiGuRE 4.31 Selecting the line to offset
4. End and restart the OFFSET command by pressing the spacebar or ↵
twice; then enter 3' ↵ ( 915 ↵ ) to set a new offset distance, and offset
the new line up (see Figure 4.32).
FiGuRE 4.32 The offset line for the 3 ′ -0 ″ (915 mm) opening
5. Start the TRIM command and press ↵ to skip the cutting edges
prompt. When asked to Select object to trim , enter F for Fence
at the command line. Draw a fence line as shown at the top of
Figure 4.33. The result should look like the bottom of Figure 4.33.