Help center
How can we help?
Find calibration, measurement, and purchase help for Ruler & Caliper. The most common answers are collected below.
Calibration
How do I calibrate the screen?
- Use a rigid, undamaged standard bank or ID card.
- If a case prevents the card from touching the screen, remove it.
- Place the card flat on the screen.
- Match the brackets to the card’s 53.98 mm short edge.
- Select Use This Calibration.
Does the app scan my card?
No. The card is only a physical size reference. The app does not use the camera and does not read, photograph, or store card details.
Why am I being asked to calibrate again?
A device or display-configuration change can make the saved scale unsuitable. Recalibrate after changing Display Zoom, moving to a different iPhone, or whenever a known reference no longer matches.
Measuring
How do I measure an object?
Keep the object flat against the usable screen edge. In Ruler mode, place the origin and end marker at the object’s edges. In Digital Caliper mode, place the left and right jaws at its edges. Use the fine-adjustment controls when needed.
Which units are available?
Millimeters, centimeters, decimal inches, and fractional inches rounded to the nearest 1/64 inch.
What does Lock Current Orientation do?
It keeps the app from rotating while you align an object. Unlock orientation from Settings when you are finished.
How can I improve a result?
Use an undamaged reference card, remove any case that blocks the screen edge, keep the object flat, align to the highlighted contact points, and compare important results with a known physical reference.
Free measurement & purchase
How does the free measurement work?
Your first completed measurement is free. You may change tools, units, and marker positions before selecting Finish Measurement. Opening the app or viewing the default value does not consume it.
How do I restore a purchase?
Select Restore Purchases on the lifetime-access screen or in Settings. Use the Apple Account that made the original purchase. Access to Apple’s App Store may be required.
Why is the price unavailable?
Check your internet connection and App Store access, then select Try Again. Device purchase restrictions can also prevent a purchase. Restore Purchases remains available.
How do I request a refund?
Purchases are processed by Apple. Review eligibility or start a request at reportaproblem.apple.com.
Offline use & reset
Can I measure offline?
Calibration and measurement work without an account or developer server. Loading a price, purchasing, and restoring require Apple’s App Store. Previously verified lifetime access remains available offline on that device.
What does Reset Calibration remove?
It removes only the saved screen calibration. It does not change your purchase, preferred unit, or free-measurement status.
Looking for policy information?
See exactly what the app stores and how the lifetime purchase works.