From Flux Developer Wiki

Rotation Property Page:

Rotate:

The Rotation page allows you to rotate the selected node. While in Rotation mode, if you drag the cursor in the vertical direction, the node will rotate about the horizontal. If you drag in the horizontal direction, the node will rotate about the vertical axis. Diagonal dragging will result in something in between.

Web3D uses an angle and an axis of rotation to define orientation. Flux Studio follows that convention. But, you don't have to think about it that way if you rotate by dragging the mouse.

Please Note that your are Rotating the Node about the Center of rotation and Scale that is defined in the TranslateNodePropPage .

There are several modifier Keys that will modify how the Node will rotate as you drag it on the scene.

Pressing CTRL while dragging will rotate the Node about the Normal of the view that your are working in.

Pressing "X", "Y", or "Z" while dragging will constrain the rotation of the Node so it rotates about the local Axis corresponding to the Key that is pressed.

Pressing SHIFT while Dragging will cause the Node to rotate about an axis that is the View Vertical, or the View Horizontal, depending on the major direction of your mouse movement.  If you drag in a Horizontal direction, then the Node will rotate about the View Vertical Axis.  If you drag in a Vertical direction, then the Node will rotate about the View Horizontal.

Also, while you are in Rotate Mode, the three Slider Bars in the Control Bar will allow you to rotate the Node about  the local X, Y, and Z Axis by using the corresponding Slider.  Note the Rotation Icon is depressed.

The rotation property sheet contains many buttons that allow you to easily manipulate the orientation of the node. You can quickly rotate the node about a positive or negative axes by 90 degrees, with the rotate 90 degree buttons. Note that these rotations are relative to the node's local coordinate system. The Align buttons allow you to snap the orientation of the node to several different orientations. Notice that you can snap relative to the Ground node, the Parent node, or the Working Group. The Snap button will align the axis to whichever orientation is closest to the current orientation. The Front, Right, Top, Back, Left, and Bottom buttons will snap to the specific orientation described by the button.