Contrast Card Generator

Print at 100%: why "Fit to Page" quietly ruins a correctly-sized card

The whole point of this tool is a pattern sized for your child's eyes at a real distance — and a single print-dialog setting, "Fit to Page," can silently shrink it. So print at 100% / Actual size and check with the 100 mm bar on every sheet.

Practitioner guidanceUpdated Jul 23, 2026For parents, educators, caregivers

Common professional practice; sensible but less formally evidenced.

In one line

The whole point of this tool is a pattern sized for your child’s eyes at a real distance — and a single print-dialog setting, “Fit to Page,” can silently shrink it. So print at 100% / Actual size and check with the 100 mm bar on every sheet.

Key points

  • Home printers can’t print to the very edge of a sheet, so PDF viewers and print dialogs often default to “Fit to Page” / “Shrink oversized pages” — which rescales everything by a few percent to fit the printable area.
  • A few percent is invisible on a photo. It matters here: a stripe width is chosen to sit just inside what the child can resolve at a given distance, so it has little margin to lose. Shrink it and the finest detail can drop below threshold (effectively invisible) — defeating the careful sizing.
  • Every sheet we generate carries a 100 mm reference bar (and a 4 in / 101.6 mm bar). Print, then measure with a ruler: 100 mm ± 0.5 mm = correct scale.
  • The fix is never the PDF — it’s the print dialog: choose “Actual size” / “100%” / “Custom: 100” and turn off “Fit to page.”

The evidence

  • [practitioner guidance] Auto-rescaling (“Fit to Page” / “Shrink to fit”) is standard, usually default, behaviour in common PDF viewers and browser print dialogs. Turning it off and printing at Actual Size is the well-established way to get true-scale output.
  • [our design opinion] Its impact on threshold-level patterns follows from the visual-angle sizing math (research §04): a design frequency placed just inside the acuity limit has, by construction, little room to shrink before it stops being resolvable. The engine’s exact-scale PDF output (points = mm × 72/25.4) is only as good as the print step that follows it.

Practical takeaways

  • Print the calibration / test page once per printer, then keep whatever setting made the 100 mm bar measure true.
  • On the first copy of any new print, measure the 100 mm bar before trusting the size.
  • If prints are consistently off by the same percentage, it’s a scaling setting — not your ruler and not the file.

Caveats & disclaimer

Non-medical enrichment tool. Individual variation in infant vision is large; the sizes are deliberately conservative design targets, not a measurement of your child. For premature, CVI, or low-vision care, follow your clinicians.