Caliper measures a headphone on an acoustic fixture and tells you how much of what you are looking at is real. Free, for Mac and iPhone.
Download Caliper on the App Store: free, and one purchase covers Mac and iPhone.
Any app can draw a curve. The hard part is knowing whether the same headphone, measured again, would give you the same curve, because if it would not, the differences you are reading belong to how it was sitting on the fixture, not to the headphone.
Most published headphone measurements are a single curve with no statement of uncertainty. Caliper asks for a few captures instead of one and spends them working out its own error budget, so every verdict it gives you is measured against a floor it actually established.
The duplicate pair. Two sweeps of one ear with nothing touched in between. Any difference between them is the instrument and the room, not the headphone, which makes it the smallest difference the run is entitled to call real. A run will not complete without one.
Seatings. Take the headphone off, put it back on, measure again. The spread between seatings is the honest uncertainty of the measurement, and it is usually larger than people expect. How many you need is derived from how much yours actually disagree, not fixed by a rule: an easy headphone may need one, a difficult one eight.
A tier, computed and never asserted. What a run earns depends on what it holds. The app says what is missing and what to do next, and a capture taken in any order counts for whatever it satisfies.
Free. No paid tier, no subscription, no in-app purchase, on both Mac and iPhone.
No account, no analytics, no telemetry, and nothing uploaded in the background. The one thing Caliper ever sends is a measurement you choose to submit, and it shows you what is being sent first. The privacy policy is specific about it.