How we measure your swing, and how often we get it right
Updated 12 Oct 2026
Birdia computes your body pose on the phone itself and flags each fault with fixed rules against a knowledge base of 47 faults with cited sources; the AI only writes the explanation. If a measurement isn't reliable, it flags nothing. In our test set of 34 real videos, the engine found exactly one swing in 33. What we haven't measured yet is how well the diagnosis matches PGA teaching pros.
Pose is computed on your phone
While you record, the phone finds your body points (head, shoulders, hips, knees, wrists, ankles) in every frame using Google's pose models, MediaPipe and ML Kit, which run on the device itself. No sensors. The video stays on your phone unless you choose to share it.
From body points to faults: fixed rules, not guesswork
From those points Birdia computes specific measurements, such as backswing-to-downswing timing, how far the hips slide, or whether the pelvis moves toward the ball on the way down, and checks them against fixed rules. Every rule comes from a knowledge base of 47 faults, and each fault cites its source: Ben Hogan, David Leadbetter, Dave Pelz, TrackMan or TPI, among others. The same measurements always produce the same diagnosis.
The AI comes in afterwards: it writes the explanation and tailors it to your level and goal. It doesn't measure anything or pick the fault, and it can't add numbers or doctrine that aren't in the knowledge base.
What the camera measures today (and what it doesn't)
Today the camera directly measures 5 faults:
Rushed tempo: the ratio between backswing and downswing time, against the ~3:1 reference (Tour Tempo, John Novosel).
The other 42 faults in the knowledge base can't be measured with a single phone camera: the clubface, the strike location or the sand don't show up in a pose. When Birdia talks about them, it presents them as a "probable cause according to the doctrine", never as something it measured.
When it isn't sure, it stays quiet
Every measurement carries a confidence from 0 to 1, and every fault in the knowledge base sets its own minimum: 0.8 for the ones a single camera sees less well, such as early extension or the putt, and 0.7 for the rest. Below that minimum Birdia doesn't flag the fault; it would rather tell you "0 faults" than guess. Anything a single camera can't measure is marked "(est.)", for estimated.
How often we get it right: the test set (gold-set)
So we don't rely on gut feeling, we keep a fixed set of videos (the gold-set) and re-run it every time the swing-detection engine changes.
33/34
Sample
34 real 7-iron swing videos: 33 filmed down the line and 1 face-on.
What is measured
Whether the engine finds exactly one swing in each video: not zero, not two.
Result (26 Jul 2026)
33 of 34 exact and 0 false detections. The one miss is the only face-on video.
Re-check (9 Oct 2026)
Swing phases come out coherent in 34 of 34 videos.
What we don't know yet
The face-on view isn't calibrated yet: with a single face-on video in the sample, that result says almost nothing. We need more videos.
The test replays recorded videos through the MediaPipe pose model. It does not cover live recording with the phone camera, which is checked separately.
We haven't yet measured how well the fault diagnosis matches what a teaching pro would say. We're building a gold-set labelled by PGA professionals: two teaching pros are filming the videos now. We'll publish the result here, with the date and the sample size.
That's why we don't quote an accuracy percentage. "33 of 34" says exactly what was measured, and nothing more.
Today we can only quote what we've measured: on 34 real 7-iron videos, the engine found exactly one swing in 33, with no false detections (26 July 2026). Diagnosis accuracy against PGA teaching pros isn't measured yet; we're preparing that test.
Does Birdia upload my videos?
No. The video and the pose stay on your phone unless you share them. For the coach's advice, the measured numbers, your profile and your question are sent, not the video.
What if the camera can't see my swing well?
If a measurement's confidence doesn't reach that fault's minimum, Birdia doesn't flag it. To measure well: phone on a tripod at hand height, 3-4 metres away, whole body in frame, face-on or down the line.
Knowledge base sources
Ben Hogan — Five Lessons: The Modern Fundamentals of Golf