A two-sided printout can contain every page and still be awkward to read because the back is rotated the wrong way. The setting to inspect is the binding edge: the edge around which you turn the sheet.

Decide how the reader will turn it

Take two pieces of scrap paper and mark the top of each page. Hold them in the final orientation, then turn them the way the finished document should work. A portrait report normally turns sideways like a book; a portrait pad may turn over the top. Landscape documents deserve their own check because the physical long edge changes position.

HP's duplex guide distinguishes Flip on Long Edge and Flip on Short Edge. The wording and location vary with the printer driver. Open the printer's properties from the application's Print dialogue and inspect the duplex choice rather than changing the document's page rotation.

Use paper that the exact printer supports for duplex operation. A driver checkbox does not make envelopes, labels or every heavy stock suitable for the automatic return path.

Prove the choice with two pages

Print one copy of two clearly numbered pages. Check the front while holding the sheet normally, then turn it around the intended edge. Both page tops should now point the way the reader expects.

If the back is upside down, change only the binding-edge option and repeat. If the back belongs to the wrong page altogether, investigate page ordering or manual reinsertion separately; rotating the text will hide the wrong problem.

Before the full run, inspect a landscape page or section break if the document mixes orientations. Save a named preset only after the actual finished stack works. Record the paper orientation and binding choice together so another person can reproduce it without interpreting an ambiguous note such as “use duplex”.

Sources: HP duplex printing guide.