How grading works
In one line: your phone finds your joints in every frame, measures how far your body is from the ideal line for that skill, and only counts the seconds you hold inside the limit. Nothing is uploaded; it all runs on your phone.
What the camera measures
- Your joints, many times a second. An on-device pose model (MediaPipe) finds shoulders, elbows, wrists, hips, knees and ankles in each frame of the live camera.
- One number per skill: degrees off the ideal. For a plank or front lever, that's how far shoulder, hip and ankle are from a straight line. For an L-sit, how level the legs are and how straight the knees. For a handstand, how far the body is from vertical. Each skill has its own rule.
- Only good-form seconds count. A level asks for a time and a form limit, for example "8 s under 12°". Seconds above the limit don't count toward the hold.
- Fair to small wobbles. The angle is smoothed over about half a second, a hold already in progress gets a little extra room, and a short dip (0.6 s by default, or more with "Wobble allowance" set to Loose in Settings) doesn't reset your timer. A real break does.
- Your experience level sets how strict it is. "Just starting", "I train sometimes" or "I train a lot" in Settings loosens or tightens the limits.
The score and the rank
Every graded hold gets a score from 0 to 100 from how long you held and how clean the form was, and a rank from Bronze to Diamond from that score. Levels unlock only when a hold meets both the time and the form limit, so a rank or level can't be earned without the hold.
What it can't see well (and how to fix it)
- Front-on filming. Film from the side. The setup check tells you to turn if it sees you face-on.
- Hands-free start. You don't need to walk back to the phone. Once the setup check is happy and you're in position for a second, recording starts by itself (you can turn this off in Settings).
- Body out of frame. Hands, hips and feet all need to be in the picture. The setup check says which part is missing before you start.
- Too far away. If you're tiny in the picture, the joints are less precise. Move the phone closer until you fill about a third of the frame.
- Dark rooms and backlight. A window behind you turns you into a silhouette. Face the light.
- Baggy clothes. Loose clothes can hide where your hips and knees really are. Fitted clothes grade more accurately.
How accurate is it?
We're running a test where an experienced coach and FormProof judge the same holds, indoors and outdoors, from different angles. When it's done, the agreement rate goes here, whatever it is. Until then, if you think a grade was wrong, send us the clip at support.skilltree@proton.me. Every wrong grade we get helps us fix the limits for everyone.
Your video stays with you
The camera picture never leaves your phone. FormProof stores only the numbers from a hold (time, angles, score). See the privacy policy.