Usage instructions:

Add either the AR202 surface-attached case from the Control tab or the MechJeb pod from the Pods tab to one of your vessels.Then use the button on the right side of the screen to access MechJeb window selection interface, and click on the buttons to activate the windows. The windows can be dragged anywhere on screen, and their position is saved and reused among all rockets.

Links:

KSP Forum thread

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