A protractor.
In your pocket.

Measure angles with the fold of your iPhone Duo. Line it up, read the angle, and save it.

Only for iPhone Duo · Now Available

Download on the App Store
When closed, drag in either direction or tap to open. Then drag either half to change the angle. You can also use the arrow keys.

A FOLD. A READING. THAT’S IT.

A little more useful.
In the real world.

A line you’ve drawn. A corner you’re curious about.
Two simple ways to put your phone to work.

01 On paper

87°
Painted illustration of a folding phone standing on paper, with its lower edges aligned to two lines and an example angle of 87 degrees.

From pencil lines to degrees.

Stand the phone on its bottom edges. Align each edge with a line on the paper, then read the angle.

02 On surfaces

135°
Painted illustration of a folding phone with each half resting against a different surface, showing an example opening of 135 degrees.

Let the fold follow the corner.

Rest each half against a surface. Fold to fit the angle where they meet, with controls on the flatter half.

Protractor reads the phone’s hinge angle. How you line up the phone, including its edges and case, affects the angle you’re measuring.

FOR THE ANGLES WORTH KEEPING

Measure now.
Remember later.

Tap Record when you’ve got your reading. Find it again in History, grouped by day with the time it was saved.

BEFORE YOU OPEN UP

Good to know.

Which iPhone do I need?

Protractor° Duo is built exclusively for iPhone Duo. It uses the phone’s folding hinge to measure the opening angle.

What does it measure?

The live hinge angle as you fold the phone. An opposite-angle reading shows 180° minus that angle. The guides help you line it up with paper or surfaces; it doesn’t measure a surface’s slope.

How accurate is it?

Use the reading as an estimate. As a rule of thumb, allow around ±5° in the hinge reading; that’s an approximate allowance, not a guaranteed tolerance. Alignment, rounded phone edges, and a case can add more error when measuring lines or surfaces.

Line up both halves carefully and hold the phone still before recording. For work that needs a precise angle, check with a dedicated measuring tool. Apple’s documentation explains that hinge updates can vary in granularity and shouldn’t be relied on for a fixed precision.

Where are my readings saved?

Your readings and preferences stay on your device. History groups your saved readings by day, and you can delete individual readings or clear them all.

Where can I download it?

Protractor° Duo is now available on the App Store for iPhone Duo. Have a question? Write to [email protected].

Protractor° Duo app icon

PROTRACTOR° DUO

Open up.
Find your angle.

Only for iPhone Duo · Now Available
Download on the App Store