Why the Last Sheet Has Fewer Crop Marks

Sixteen pages, six to a sheet. The first two sheets look right. The third holds four pages instead of six — and its bottom row has no crop marks under it. The side marks are there. The top marks are there. The bottom edge, which is the one the guillotine operator sets the back gauge from, has nothing.

Counted on a real 2 × 3 layout: 20 ticks, 20 ticks, then 14. Six missing, all on the same edge, all on the last sheet.

Crop marks are not drawn around every cell. They are drawn on the outside edges of the block — that is what makes a sheet of cards cuttable in a stack rather than covered in hairlines between the pieces.

So when the grid is planned, each cell is told which of its four edges are outside edges. A cell in the middle of a 2 × 3 grid has none. A cell in the bottom row has one: its bottom. That mask is computed from the grid's shape — two columns, three rows — because the shape is what is known at planning time.

Then the pages are dealt into the cells, and on the last sheet there are only four. The two empty cells in the bottom row contribute nothing at all: no page, no marks. And the cells in the row above them — the last row that actually got filled — were told, correctly for a 2 × 3 grid, that there is a row beneath them. So they suppress their bottom ticks, as a middle row should.

The result is a sheet whose last filled row behaves like an interior row on a sheet where it is the outside edge. The information that would fix it — "this row is now the bottom" — exists only after the pages are dealt, which is after the mask was decided.

Six missing ticks out of twenty sounds like a rounding error. It is not, because of which six.

A guillotine is set by registering the sheet against a back gauge and a side lay, then cutting to marks. The bottom edge of the block is a reference, not a decoration. Lose it and the operator has three options, all bad: measure from the sheet edge and inherit whatever the trimming of the parent sheet did, extrapolate from the side marks and hope the grid pitch is exactly what they think, or set that one sheet by eye.

On a short run the last sheet is often a proof or a make-ready, so the error propagates. On a long run it is the one sheet that does not match the others, which is worse — the operator has settled into a rhythm by then.

1. Choose a grid that divides your page count

The cleanest fix, and free. Sixteen pages 4-up is four full sheets; sixteen pages 6-up is two full sheets and a ragged one. If the count and the grid are both yours to choose, pick a pair that divides evenly and there is no partial sheet to have a problem with.

This is not always possible — a prime page count, or a fixed grid the finisher requires — which is why the other two exist.

2. Mark every cell edge

Turn on interior marks and every cell gets ticks on all four edges, including the last filled row's bottom. The short sheet is fixed.

The cost is real and lands on every sheet, not just the short one. Interior ticks sit on the trim line of the piece next door — a hairline one stroke width from printing on the product — and they roughly double the marks on a full sheet. Measured on the same 2 × 3 job: 48, 48, 32 instead of 20, 20, 14. Most finishers dislike them; a few insist on them. Ask yours.

3. Pad the last sheet deliberately

Add blank pages to fill the final sheet, so there is no ragged row. This costs paper and it costs the operator a step — they now have to pull the blanks before the job goes on — but it does produce a sheet that looks exactly like the others, and for a long run that consistency can be worth more than the sheet.

The underlying behaviour is the same as in other imposition tools — it falls out of how mark masks are computed — so the useful thing is not to pretend otherwise but to say so before the sheet is printed. The panel names the shortfall and what it means:

6-up on A3 · 2 × 3 · last sheet holds 4 of 6 · its bottom row prints no marks — cut it from a full sheet

That note appears only when the count does not divide the grid and marks are on — the two conditions that produce the problem. Change the grid to one that divides and it disappears, which is the nudge toward the free fix.

The interior-mark option is there as an advanced toggle, Mark every cell edge, and its own description says what it costs rather than presenting it as a straight improvement. When it is on, the warning drops to a plain statement of the count, because the marks are no longer missing.

Step & Repeat never shows any of this: it fills every cell from the same page, so its last sheet is never short.