To the right of the transform buttons on the Main toolbar are six controls, collectively referred to as the transform managers. These controls modify the action of the three transform buttons.
You use the transform manager controls to specify:
The transform center about which you apply the transform.
The axis constraints that restrict the transform along one or two axes.
Certain terms are used in the description of transforms and the transform managers.
An axis is a straight line along which an object is moved or scaled, or about which an object is rotated. When you work in 3D, you use three axes, labeled X, Y, and Z, that are oriented 90 degrees from each other.
A transform coordinate system specifies the orientation of the three X, Y, Z axes used by a transform.
For example, in the World coordinate system, as seen from the Front view, the X axis runs horizontally from left to right, the Y axis runs from back to front, and the Z axis runs vertically, from bottom to top.
On the other hand, each object carries its own Local coordinate system. If the object has been rotated, its Local coordinate system will be completely different from the world coordinate system.
The transform center, or pivot point, is the spot about which a rotation takes place, or to and from which a scale occurs.
Using the transform managers on the main toolbar, you can specify any combination of axes, transform coordinate systems, and transform centers.
An axis tripod appears in the viewports when you select one or more objects, to assist you visually in your transforms. This tripod consists of three lines, labeled X, Y, and Z, and shows you three things:
The orientation of the tripod reveals the orientation of your coordinate system.
The location of the junction of the three axis lines shows you where your transform center is.
The highlighted red axis lines show you the axis or axes to which the transform is constrained. For example, if only the X axis line is red, you can move objects only along the X axis.
Note: The Transform gizmo normally supplants the axis tripod for selections when a transform mode is active. Besides providing all of the above functions, it lets you specify the transform axis or axes without explicitly setting constraints; see Using the Axis Constraints. For more on the Transform gizmo, see Using the Transform Gizmo.
You can toggle the display of the axis tripod in all viewports by choosing Views menu > Show Transform Gizmo, or by pressing the X key.
The state of the three transform managers (coordinate system, center, and axis constraints) is stored with each type of transform. When you switch from Move to Rotate to Scale, the transform managers change to whatever combination they were in when you last used that transform.
For example, if you click Rotate and set the transform managers to Screen, Selection Center, and Y constraint, when you click Move, the controls might shift to View, Pivot Point, and XY constraint (whichever combination was set the last time you used the Move button). When you go back to Rotate, the controls revert to Screen, Selection Center, and Y constraint.
Tip: To avoid surprises, always click the transform button first, and then set the transform managers. If, instead, you first set the transform managers, their settings are likely to change as soon as you choose a new transform button. One way to remember this is always to set the transform and managers by working from left to right on the main toolbar. Alternatively, you can turn on Customize menu > Preferences > General tab > Reference Coordinate System group > Constant, which keeps the transform manager settings the same for all transforms.