Placement on a poster
Edges, headlines, and the trim.
poster preview is an A-proportion frame with a headline and a code you can drag. The status line reports pixels from the code to each edge and the gap under the headline. Keep the quiet zone off the type and off the trim. A code in the bleed gets cut.
The preview is not a color-managed proof. Print the test sheet at 100% scale. A “fit to page” setting in the print dialog shrinks the millimetre sizes and makes the test meaningless.
Measure one code on the paper with a ruler. If the 30 mm square is not 30 mm, the printer scaled the page.