Measures angles with the Duo's hinge: fold it to fit a sketch or a corner, then save it
Does Protractor°: Angle Finder work on iPhone Duo?
Yes, it runs only on iPhone Duo, says its developer: fold the phone to fit an angle, read the hinge angle and its opposite, and save the reading. It needs iOS 27.1.
- App Store confirmedJust2us, the developer, in a submission to FoldHunt on October 22, 2026, saying the app, which it calls Protractor° Duo, was tested in the iPhone Duo simulator but not on a device, and that readings are meant as everyday estimates, since Apple documents the hinge angle's accuracy as ±5°. The App Store seller is Just2us Pte Ltd. The App Store description says the app requires iPhone Duo with iOS 27.1 or later and measures with the phone's folding hinge. The release notes for version 1.1 (released October 22, 2026) change the free trial, keep readings from 80° to 100° free after it, and don't mention the Duo by name.
Adapted for the fold
- Closed · Outer display
How to line it up
Closed, the cover shows how to open the phone and line it up for a measurement.
- Book · Partly folded
Fold it to fit the angle
Unfold the Duo partway and the display shows the hinge angle in large numbers, with the opposite angle (180° minus it) below, changing as you move the halves. Stand it on its bottom edges along two lines on paper, or rest each half against a surface, then tap Record to keep the reading in History, grouped by day.
About Protractor°: Angle Finder
Protractor°: Angle Finder, which Just2us also calls Protractor° Duo, uses the iPhone Duo’s hinge as a protractor. To measure a drawing, you stand the phone on its bottom edges and line each edge up with a line on the page; to measure where two surfaces meet, you rest one half against each and fold it to fit. The display shows the angle and its opposite as you adjust, and Record saves the reading to History, grouped by day, where you can delete readings one by one or all at once. Readings stay on the phone.
It only works on the iPhone Duo with iOS 27.1 or later, because it measures with the folding hinge. Closed, the cover explains how to open and line up the phone. Just2us says to treat readings as estimates, allowing about ±5° in the hinge reading, more with careless alignment, the phone’s rounded edges or a case. The app is free to download with a trial; afterwards, angles from 80° to 100° stay free.
Evidence reviews
What we checked, when, and what the evidence establishes. Each record preserves the support label at that check.
· App Store page reviewed
App Store confirmed · iphone-duo
The App Store description mentions iPhone Duo: "Use your iPhone Duo as a protractor." (version 1.1, released October 22, 2026).
App version: 1.1.
Store text only: we haven't seen the app running, and the store page doesn't show how each pose is used.
View reviewed evidence ↗· Developer media reviewed
Developer claimed · iphone-duo
Watched frames across the developer's 42-second YouTube film, a 3D render of a Duo with the app's screens on it: the cover reading Open up, Find your angle; the phone standing on its edges over a roof sketch at 87°; and the phone open to 165°, 142° and 135° in the corner of a wooden box, with a Record button and a History list of saved readings.
Poses shown: Closed, Book. These are observations of the evidence, not a test of every interaction.
App version: Not recorded in this evidence.
A render, not a capture from the simulator or a device, so it doesn't show the app running. The website's pictures are illustrations and an interactive demo, and the X post has no media. No app version is shown and no build was tested.
View reviewed evidence ↗
Watch it unfold
On X
We gave the iPhone Duo’s fold another job. Protractor° Duo uses the hinge to measure angles. Line up your phone with a sketch or corner, then save the reading for later. just2us.com/protractor/
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Is this your app?
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Sources: Protractor°: Angle Finder on the App Store (apps.apple.com) · Protractor° Duo on the Just2us website (just2us.com) · Just2us Labs on X (x.com) · iPhone Duo Protractor App: Measure Angles with the Fold (YouTube) (youtube.com)
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