Phoebe guidesTry this in the phone motion and tilt lab, where you change the phone tilt and see the orientation reading and level indicator.
1. Accuracy is an uncertainty radius
coords.accuracy is the provider's 95% uncertainty estimate in metres. The browser does not promise which radios, cached values, inertial inputs, or databases produced it.
2. See why radio scale is difficult
Spread power over areaS=Pt/(4πd²).
Express the ratio as lossFSPL=(4πd/λ)², or 20log10(4πd/λ) dB.
3. Bound timing without overclaiming
Invert the chip rate1/(1.023 Mchip/s)=0.978 µs per chip.
Multiply by light speed0.978 µs × 3.00×10⁸ m/s ≈ 293 m.
Receivers estimate sub-chip timing and combine several corrected pseudoranges. One chip's travel distance is a physical scale, not a final position-accuracy guarantee.
4. Reproduce the chapter decisions
Both fixes are much coarser than the stated distinction. Request a better fix or defer; do not make the location decision anyway.
5. Preserve what the API actually says
Record coordinates, timestamp, radius, permission state, request settings, and whether the value was fresh enough for the task. enableHighAccuracy is a hint, not a promise of GNSS or a particular precision.
6. Check yourself
What does a 25 m accuracy value mean here?
Can a 40 m radius answer a 10 m nearest-point question?
Does 293 m per C/A chip set GPS accuracy?
These are the chapter inputs, worked results, and named teaching assumptions.
- 1575.42 MHz carrier
- Frequency, sample rate, or event rate
- about 20,200 km path
- Distance, wavelength, or size
- 182.5 dB free-space loss
- Gain, loss, margin, or level ratio
- 1.023 Mchip/s timing scale
- Time, interval, or service-life value
- 293 m chip travel
- Distance, wavelength, or size
- 25/5 plus 40/10 task ratios reproduce the chapter
- Percentage, ratio, or gain
They do not identify the browser's hidden provider or predict its position error; Under the Hood keeps those system limits.