Why does a viewport show the wrong part of my drawing?

[indiancad]

I recently ran into a layout where the viewport was showing the wrong area of the model, even though the model itself was correct.

 

At first I thought the viewport had been moved or resized.

 

The simple fix was to activate the viewport and use ZOOM > Object or PAN to position the view correctly.

 

One thing I also check now is whether the viewport is locked, because a locked viewport can make it confusing when trying to adjust the view.

 

It reminded me that sometimes the drawing is fine and the problem is only with the viewport settings.

 

How do you normally troubleshoot a viewport that suddenly shows the wrong area?