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The web speedometer is small. The questions around it are not. These posts cover the physics, the regulations, and the practical tests you can do with the phone in your pocket.
2026-06-01 · 10 min read
Most Android phones can show your speed without a single Play Store download. Google Maps, Android Auto, the browser, and the apps worth installing, ranked by how much friction each one costs you.
2026-06-01 · 7 min read
KPH is kilometers per hour, the speed unit used by most of the world. What it means, how it differs from MPH, the exact conversion, and the mental math to switch between them in a second.
2026-06-01 · 9 min read
The "10% plus 2 mph" rule is guidance, not law, and it varies by country. What camera tolerance actually is, why your speedometer reading high already eats into it, and why GPS is the honest number.
2026-05-16 · 10 min read
Every smartphone has the hardware to be a precise speedometer. Choosing among hundreds of apps is the hard part. An honest comparison of the options that deserve your attention.
2026-05-16 · 9 min read
Most cars do not need recalibration. The 4 mph optimistic dial at 70 mph is the law working as intended. When you actually need to recalibrate and what it costs in 2026.
2026-05-16 · 8 min read
The Apple Watch has a GPS chip but no single speedometer app. Three native ways to see speed (Workout, Maps, Compass), plus third-party options and accuracy notes.
2026-05-16 · 9 min read
The 3 to 5 mph gap between Google Maps and your dashboard is not a bug. Each one is measuring a different thing, and only one of them is the real ground speed.
2026-05-16 · 10 min read
The iPhone has a perfectly good GPS chip. Getting it to show you a speed reading is the hard part. Four ways to do it on a stock iPhone, three of them free.
2026-05-04 · 9 min read
Factory speedometers are calibrated to read 2 to 5 mph high. Here is the regulation, the math, and why a GPS reading is the honest one.
2026-05-04 · 8 min read
Modern phones report speed within ±0.5 to 2 mph. The accuracy comes from Doppler shift, not just position differences. A practical look at the numbers and the limits.
2026-05-04 · 7 min read
A 10-minute speedometer test you can do with your phone. Compare your dashboard against GPS at three speeds, calculate the offset, and decide whether to recalibrate.