ZeroToSixty turns your iPhone into a GPS-based performance timer. Measure your 0–60 MPH (or 0–100 KM/H) time, run the quarter mile, and keep a history of every attempt. This guide covers how to use the app and how to fix the most common problems.

Getting Started

What you need

• An iPhone with GPS (any model with cellular or a dedicated GPS chip)
• A clear view of the sky for the best GPS accuracy
• Location permission granted to ZeroToSixty

First launch

1. Open the app. You’ll see a one-time notice explaining that iOS delivers GPS speed about once per second.
2. Tap Got it.
3. When prompted, allow location access by tapping Allow While Using App.
4. Mount your phone securely in your vehicle (windshield or dash mount works best).

How to Record a Run

1. Open the Speedometer tab.
2. Choose your target: 0-60 (MPH) or 0-100 (KM/H).
3. Choose a start mode:
   • Stop — timing begins the moment you start moving from a standstill.
   • Rolling — timing begins when you cross 5, 10, or 15 MPH.
4. Tap Arm. The timers switch to the orange Armed state.
5. Begin your run. The timer auto-starts when you cross the start threshold and stops when you hit the target speed (or complete the quarter mile).
6. The result is saved automatically to History when the run is marked Done.
7. Tap Reset to clear and prepare for another run.

Reading the screen

• Big number — current speed in your chosen unit.
• Progress bar — how close you are to your target (green → yellow → red).
• Heading row — compass direction and your top speed for the session.
• Timer cards — show state badges: Idle, Armed, Running, Done.

Settings Explained

Speed Unit

Tap the gauge icon to switch between:

• MPH (GPS) / KM/H (GPS) — speed as reported directly by iOS. Smoothest reading.
• MPH (Corrected) / KM/H (Corrected) — speed calculated from the distance between GPS fixes. Reacts faster but can be noisier.
• M/S — meters per second, useful for unit comparisons.

Target Speed

Switch between 0-60 MPH and 0-100 KM/H using the flag icon.

Start Mode

• Stop — best for a true 0–60. Requires the phone to see you below ~1 MPH before arming.
• Rolling — start the timer at 5, 10, or 15 MPH. Useful when you can’t safely launch from a dead stop.

Troubleshooting

The speed reading lags behind my real speed

This is expected. iOS provides GPS speed updates only about once per second, so the on-screen number can trail your actual speed by up to a second.

Note: the 0–60 and quarter-mile times use precise GPS timestamps, not the displayed value. Your saved times are accurate even if the number on screen looks behind.

If you want a more responsive (but noisier) reading, switch the speed unit to MPH (Corrected) or KM/H (Corrected).

The timer never starts

• Make sure you tapped Arm. The timer cards must show the orange Armed badge before a run.
• If using From Stop mode, the app waits until you’re nearly stationary before triggering. Come to a complete stop, then accelerate.
• If using Rolling Start, you must cross the rolling threshold (5, 10, or 15 MPH). Check that you’ve selected the right threshold.
• Confirm location access (see below).

The speedometer shows 0 and never updates

• Check location permission. Open Settings → Privacy & Security → Location Services → ZeroToSixty → set to While Using the App.
• Make sure Location Services is on globally. Settings → Privacy & Security → Location Services → toggle on.
• Step outside or away from tall buildings. GPS doesn’t work indoors or in parking garages.
• Disable Low Power Mode during a run — it can throttle background sensors.
• Restart the app by swiping it away from the App Switcher and reopening.

My 0–60 time looks too fast or too slow

• GPS multipath. Tall buildings, tunnels, and tree canopies bounce GPS signals and can produce inaccurate speed samples. Run on open road for best results.
• Cold start. Wait 30–60 seconds after launching the app for the GPS to fully lock on before running.
• Phone placement. Mount the phone where it has a clear view of the sky. A dashboard or windshield mount is best. Stuffing it in a pocket or center console can degrade signal.
• Rolling start with a low threshold. Even at 5 MPH, your true 0–60 time will be slightly shorter than the elapsed time shown.

The quarter-mile distance never reaches 1320 ft / 402 m

• The app accumulates distance from each GPS fix. Poor signal can drop fixes and stall the distance counter.
• Make sure you actually traveled the full distance — the run only marks Done when 402 m have accumulated.
• If a single fix jumps more than 200 m (likely a GPS glitch), that delta is ignored to protect the run from spikes.

Top speed seems wrong

Top speed records the highest GPS-reported speed during the session. It’s reset whenever you tap Reset or Arm a new run.

History shows nothing after a run

• A run is only saved when the timer reaches the Done state. If you hit Reset before the run completed, it isn’t saved.
• Pull down to refresh the History tab, or switch tabs and back.
• If the issue persists, force-quit and reopen the app.

How do I delete a run from History?

• Swipe left on any run for a delete button.
• Or tap Edit in the top-right and tap the red minus next to each run you want to remove.

How do I filter History?

Tap the filter icon in the top-left of the History tab and choose All, 0–60 MPH, 0–100 KM/H, or Quarter Mile.

The screen keeps turning off mid-run

The app already prevents auto-lock while the Speedometer tab is visible. If your screen still locks:

• Make sure you haven’t switched away from the Speedometer tab.
• Check that Auto-Lock in iOS Settings → Display & Brightness isn’t being overridden by Low Power Mode.

CarPlay doesn’t show ZeroToSixty

• Connect your iPhone to your car (wired or wireless CarPlay).
• In your car’s CarPlay screen, look for the ZeroToSixty icon. You may need to customize the CarPlay app order in iOS Settings → General → CarPlay → [Your Car] → Customize.
• Some older head units do not support newer CarPlay templates.

The compass heading is wrong or stuck

• Calibrate the compass by waving your iPhone in a figure-eight motion.
• Move away from large metal objects (engine blocks, speakers, magnetic mounts) which can interfere with the magnetometer.
• Confirm Compass Calibration is enabled in Settings → Privacy & Security → Location Services → System Services.

Numbers don’t match my car’s speedometer

Car speedometers are required by law to read slightly high — typically 2–5% over actual speed — so the GPS-based reading in ZeroToSixty will usually be slightly lower than what your dashboard shows. The app’s GPS reading is closer to true ground speed.

Safety & Legal

• Never operate the app while driving. Have a passenger handle Arm/Reset, or use a closed course.
• Only run performance tests on a legal, closed course or private track.
• Obey all traffic laws. The developer is not responsible for misuse.

Privacy

• ZeroToSixty uses your location only while the app is open, only to measure speed and distance.
• Location data is never uploaded, shared, or stored off-device.
• Run history is stored locally on your iPhone using Apple’s SwiftData. Deleting the app removes all run history.