(or press SHIFT) to force lines to draw at a 15-degree angle. This constraint is useful for drawing lines (and object edges) that are perfectly horizontal or vertical.
The Constraint buttons restrict, or constrain, the way in which objects are drawn. A selected button remains on until you click it again to turn it off.
Constraining with the Keyboard
You can use keystrokes to activate constraints. Keystrokes activate a constraint only while the key is pressed.
You can use a key to toggle the effect of a constraint button. For example, if you press and hold CTRL while the Angle Constraint button is selected, you turn off the constraint.
Constraining to a 15-degree Angle
You can use the Angle Constraint button
(or press SHIFT) to force lines to draw at a 15-degree angle. This constraint is useful for drawing lines (and object edges) that are perfectly horizontal or vertical.
This button also forces horizontal and vertical movements, and rotations and skews of 15-degree increments.
Constraining to a Square or Circle
Use the Proportional Constraint button 
(or press SHIFT) to force rectangular or elliptical shapes to draw as squares or circles, respectively.
Reversing the Drawing Direction
Use the Reverse Direction button 
(or press CTRL) to reverse the direction Designer normally draws objects created from a single side (for example, drawing a square from a single side). See the specific drawing method you are using for details.
Use the From Center button 
(or press CTRL) to force Designer to draw the object from the center outward. Drawing from the center can be useful when you want the center of the object to be at a particular point.
