To edit tangent constraint channels with the Channel Box

1. In the scene, select the constrained object.
2. Set the channels.
3. Click the name of the channel you want to edit.
4. In your scene, -click and move the mouse to the left or right. By moving the mouse, you interactively change the value of the selected channel. As you move the mouse, note that pressing the key gives you finer control, and pressing the key gives you less control.