Phone-screen measuring: calibration and viewing-angle checks

Use the card as a physical standard

A standard payment card or ID-1 identification card is 85.60 mm wide by 53.98 mm high. Use a flat card with square, undamaged edges. A warped card, thick sleeve, raised embossing under the contact area, or novelty card can spoil the calibration.

1. Remove the phone case if it prevents the card from lying flat on the screen.
2. Set the phone on a firm, level surface.
3. Place the card in the shown orientation and align both long edges—not one corner.
4. Adjust until the exact-size red reference is covered and the touching green clearance edge is just visible outside.
5. Save the calibration, then reopen the gauge and confirm it did not move.

Why larger parts exaggerate viewing error

A tall bolt or fitting holds its measured edges above the glass. If you look from the left, the top of the part appears shifted to the right; looking from the right reverses the error. The wider or taller the part, the more convincing that false size can look.

Center your eyes over the measured section and judge both contact edges together. If one edge appears correct only when you lean to one side, reset the part and your viewing position.

Put the intended surface on the reference

• Bolt diameter: the threaded shaft lies sideways; compare the outside thread crests.
• Nut or bolt head: compare opposite flats, not corners.
• Open-end wrench: compare the inside jaw faces.
• Six-point socket: compare the internal hex, not the round outside body.
• Washer: compare the inside circular hole.
• Smooth pipe: compare the straight cylindrical body, not a fitting or threaded crest.

When to repeat the measurement

Repeat after orientation changes, browser zoom, a display-size setting change, or any time a known part suddenly measures differently. If two standard sizes remain inside the comparison window, that is useful uncertainty—not a reason to force one answer. Confirm with pitch, markings, or a known mating part.