This Gizmo let's you overscan your plates in Nuke after undistorting, and calculates the required resolution and camera scale needed to compensate for the overscan. This is very useful when 3D tracking in Nuke and sending the undistorted plates to your 3D department. I also use this Gizmo when 2D tracking a shot, but need to know the correct overscan I'll need from the 3D team that will cover the move.
The overscan percentage value can be input in Nuke's camera in the window scale u and v knobs. In Maya it's the Camera Scale attribute in the camera.
Gizmo / mS_Overscan