your phone, eight numbers

Press a button. Your phone yields eight numbers. The browser never says which sensor coughed them up — GPS satellites overhead, a WiFi BSSID lookup, cell-tower triangulation, all of the above — only the summary. Below is that summary, live, from your phone, on this page.

A few opinions, since the spec doesn't ship with any.

Accuracy is a 68% radius, not a fence. The phone is saying "there's a two-in-three chance I'm inside this circle". The other third is just being honest about that.

Altitude is the runt of the litter. GPS satellite geometry strongly favors horizontal — the error ellipse is taller than it is wide. Half the devices in the world report null for altitude entirely, and the browser shrugs and passes the shrug along.

Heading is null when you're still. Phones don't compute direction from compass alone for navigator.geolocation — they want a velocity vector first. So heading appears the moment you start walking, and disappears when you stop. The compass is in the browser, but it lives somewhere else: DeviceOrientationEvent.

Fix age matters more than people realise. A fresh fix is the truth at this moment. A two-minute-old fix is the truth at some moment, and you've been walking since. Watch mode keeps it warm; one-shot mode is a snapshot that ages.

The browser hides the source. You don't get to see whether the latitude came from a sky view of seven satellites or from a WiFi BSSID whose fingerprint matched a database in Mountain View. Mostly this is fine. Sometimes — accuracy: 1500m indoors — it's the only clue you have.

That's the whole API: getCurrentPosition for one shot, watchPosition for a subscription, clearWatch to hang up. Eight numbers come back. The rest is interpretation.