HUD speedometer — live GPS speed for your windshield

HUD is short for heads-up display. Lay the phone screen-up on the dashboard and the windshield reflects the numbers back at you, so your speed appears to hover over the road instead of sitting behind the steering wheel. Nothing is being projected — it is the glass doing the work, the same reflection you already get from a brightly lit dashboard at night.

That is what the Mirror button is for. A reflection reverses left and right, so the display has to be reversed first to read correctly in the glass. The page opens the normal way round so you can read it while you set up. Tap Mirror just before you lay the phone down.

It works best after dark, on a clean windscreen, with the screen at full brightness and something dark underneath it — a pale dashboard washes the reflection out. In daylight it is usually too faint to read at all. A non-slip mat stops the phone sliding away on the first corner, and full screen removes the browser chrome so only the speed is reflected.

Set the display up before you move off, never while driving. The screen stays awake by itself while tracking, so there is nothing left to touch once you are going.