Long-edge vs short-edge duplex printing

The flip option describes the physical edge around which a sheet turns. It is separate from the movement of content inside a PDF. A correct flip can give upright backs while the artwork is still offset. An incorrect flip can leave the back upside down even when its center is correct.

Start with the actual page shape

For a portrait sheet, the long edges run down the left and right. Turning around a long edge resembles opening a book. Turning around a short edge resembles lifting a page on a top-bound pad. On a landscape sheet, those edge positions change: its long edges are at the top and bottom.

These descriptions explain the geometry, rather than prescribing a printer menu choice. The reading direction of the intended document matters. Driver labels and manual refeeding behavior can vary. Print a marked pair and verify which way the back reads on your equipment.

Why a measured offset changes sign

When you hold the front toward you and look through the paper, you see the reverse side of the back artwork. Its coordinates are reflected around the flip edge. A movement to the right in the back PDF may appear to move left when viewed through the front. That is why a guided measurement is different from a direct PDF movement.

A worked portrait example

The dashed back marks appear 2 mm to the right and 1 mm below the front marks when you look through the front. The page is portrait and the printer is set to long-edge flip. Enter +2 horizontally and +1 vertically in measured mode. BackAlign proposes moving even PDF pages +2 mm right and −1 mm down, meaning 1 mm up in their own PDF view.

Do not enter the correction a second time as though it were another observation. Measure the original proof, export once, and print a new proof. The downloaded settings contain numbers, not evidence that a physical printer has been calibrated.

When to use direct movement

Choose direct mode if you already know the required movement as viewed while reading the PDF itself. In that mode, +2 right and +1 down mean exactly those movements on each selected PDF page. The tool applies no mirror conversion. Direct mode also offers odd, all or specific page selections.

The guided mode assumes ordinary interleaved page order: page 1 front, page 2 back, page 3 front, page 4 back. It does not reorder pages, mirror artwork or impose a booklet. If your document uses a different arrangement, prepare the correct page order first or select pages deliberately in direct mode.

References and verification

Adobe: PDF print sizing options. Geometry and worked examples on this page are BackAlign’s own calculations. Digital PDF transformations are tested; physical printer output has not been verified.