Coordinating turns visually

Since my simulator is not full-motion, I can't judge the quality of a
turn by feel. However, it stands to reason that I should be able to
detect slipping or skidding visually, by watching how the horizon
moves out the window--after all, any movement of the aircraft will
change the view out the window. Can anyone offer suggestions on how I
can best recognize a coordinated turn by looking outside the aircraft?

My guess is that, if the horizon doesn't move in a direction other
than horizontally (aligned with the horizon) the turn is coordinated,
but I'm not sure about this (I'm still doing experiments).

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