How to record a video we can actually measure

1. Stand the camera square to the bike

Every angle in your report — hip, knee, back, elbow — is measured from a side-on view. A camera that's even a little angled in or out measures a shorter leg than you actually have, and the whole report shifts with it.

• Put the phone level with your hip, not on the floor and not up high.
• Stand it 2–3 m away, directly out to the side — square on, not diagonal.
• Film in landscape, so the whole bike fits without stepping further back.

2. Don't hold the phone

The analysis assumes the camera stays put, so anything the camera does gets read as something your body did. A tripod is ideal; a shelf, a windowsill or a chair with the phone leant against a book all work just as well.

3. Fit the whole bike in frame — both wheels included

Your wheels are the ruler. Their rim diameter is a known, exact standard, so the analysis uses both wheels to work out how many millimetres a pixel is worth. Crop one out and the measurements lose their scale.

• Both wheels fully visible, touching neither edge of the frame.
• Your whole leg in shot — hip to ankle — with nothing crossing in front of it.
• Head and shoulders in frame too; back and elbow angles need them.

4. Clear the bike, and wear something fitted

These two are the most common causes of a bad reading, and both are fixed in ten seconds before you start. They are not hypothetical — each one was traced from a real scan that came back wrong.

• Bottles, pumps, bags and tools mounted near your pedalling leg — a fixed object close to your leg's path gets mistaken for a joint.
• Baggy shorts — loose fabric bunching at the top of the pedal stroke pulls the knee measurement onto the hem instead of your knee.

5. Ride normally for 10–20 seconds

Long enough to capture several clean pedal strokes, short enough to upload fast. Ride the way you actually ride — the point is to measure your real position, not your best one.

• Steady, even cadence — no surging, no coasting.
• Hands where you normally hold them for the riding you're asking about.
• Look ahead, not at the camera.

6. Light it evenly, keep the background plain

Anything that makes your outline hard to pick out makes the measurement harder. You don't need good lighting — you need even lighting.

• Light from the side or front, not from a bright window directly behind you.
• A plain wall beats a cluttered garage.
• Wear something that contrasts with the wall behind you.

7. Optional: a second clip from the front

A side-on camera physically cannot see your knees tracking in or out, or your pelvis rocking side to side. If you want those, record a second 10–20 second clip head-on, same rules as above, and add it to the same scan.