Creating Your First Drawing - Mastering AutoCAD for Mac - page 33

F -Z and U ↵ If you accidentally change something in the drawing and want to reverse
that change, you can use the standard F-Z keystroke to back up one operation. You can also
type U ↵ at the Command prompt. Each time you do this, AutoCAD undoes one operation at
a time, in reverse order. The last command performed is undone first, then the next-to-last
command, and so on. The prompt displays the name of the command being undone, and the
drawing reverts to its state prior to when that command was issued. If you need to, you can
undo everything back to the beginning of an editing session.
Undo If you want more control over the way Undo works, you can use the Undo command,
which allows you to “bookmark” places in your editing session that you can “undo” to.
Type Undo ↵ and you'll see the Enter the number of operations to undo or [Auto/
Control/BEgin/End/Mark/Back] <1>: prompt. You can enter a number indicating the num-
ber of steps you want to “undo.” Use the Mark option to “bookmark” a location; then use Back to
undo your work to that “bookmark.” You can use Begin and End to mark the beginning and end
of a set of operations that will be undone all at once. Control offers options to control the behav-
ior of the Undo command. Auto is an option that is on by default and causes AutoCAD to undo
the action of the whole command rather than the individual actions within a command.
Redo If you accidentally undo one too many commands, you can redo the last undone com-
mand by pressing F-Y or by typing Redo ↵.
Palette toggle If a palette has been turned off, you can turn it back on by choosing Tools 
Palettes. A list of palettes appears. Click the palette that you want to turn on.
Specifying Polar Coordinates
To enter the exact distance of 3 (or 9 metric) units to the right of the last point you selected, do
the following:
1. Click the Line tool in the Tool Sets palette, or type L ↵.
2. Click a point slightly to the left of the center of the drawing area to select the start point.
3. Type @3<0 . Metric users should type @9<0 . As you type, the letters appear at the
Command prompt.
4. Press ↵. A line appears, starting from the first point you picked and ending 3 units to the
right of it (see Figure 2.6). You've just entered a relative polar coordinate.
The “at” sign (@) you entered tells AutoCAD that the coordinate you're specifying is from
the last point you selected. The 3 (or 9 metric) is the distance, and the less-than symbol (<) tells
AutoCAD that you're designating the angle at which the line is to be drawn. The last part is the
value for the angle, which in this case is 0 for 0°. This is how to use polar coordinates to commu-
nicate distances and directions to AutoCAD.
If you're accustomed to a different method for describing directions, you can set AutoCAD to
use a vertical direction or downward direction as 0°. See Chapter 3 for details.
Angles are given based on the system shown in Figure 2.7, in which 0° is a horizontal direc-
tion from left to right, 90° is straight up, 180° is horizontal from right to left, and so on. You can
specify degrees, minutes, and seconds of arc if you want to be that exact. I'll discuss angle for-
mats in more detail in Chapter 3.