UCS Rotation Dilemma

Hello everyone. I have read through several pages of threads and searched on the topic, but I have not found an answer that solves my problem in a way I can decipher. Nonetheless, I apologize if this has been covered before, and I hope the general section suits a question this sort.

Every object on the drawings I work with is rendered according to its northerly and easterly coordinates in relation to a single origin. It's a huge site with thousands of drawings, and all drawings are done in relation to the same origin. With most drawings I get, the UCS icon indicates the Y-axis being positive in the up direction and the X-axis being positive to the right, but I've recently been assigned a drawing that displays the X-axis being positive in the up direction, and the Y-axis being positive to the left. I would like to know how this was achieved. I do not think it's a matter of creating a new UCS, because UCS sets a new coordinate origin, but the coordinate origin for this drawing is no different from any of the other drawings (if I copy the contents of an adjacent drawing and paste them to their original coordinates in this drawing, they line up just fine even though the UCS icon appears to be rotated). How do I enact the AutoCAD equivalent of merely tilting my head 90° to the right (or 270° to the left) while working?

Thank you, and any help would be greatly appreciated.

Sounds like someone made a new rotated UCS, used the Plan command, and then set the UCS back to World, or applied a twist with the Dview command. To return it so Y is pointing up, use the Plan command.

Sounds like someone made a new rotated UCS, used the Plan command, and then set the UCS back to World, or applied a twist with the Dview command. To return it so Y is pointing up, use the Plan command.

Looks like a twist had been applied with Dview. It's a great relief to find that it was something so simple. My brain is experiencing a feeling like the sick levity of having just passed a kidney stone. Thank you, lpseifert!