Speed Dash

Speed Dash - Accurate GPS Speedometer

Purpose

Speed Dash is designed to help users verify the accuracy of their vehicle's speedometer by comparing it with GPS-based speed measurements. Most vehicle speedometers have a built-in margin of error (typically showing 5-10% higher than actual speed), and this app allows you to see the difference in real-time.

Key Features

Real-Time GPS Speed: Displays your current speed based on GPS data
Multiple Units: Switch between km/h, mph, m/s, and knots
Speed History Graph: Visualizes speed changes over time
Altitude Tracking: Shows your current altitude and changes over time
Signal Quality Indicator: Displays GPS accuracy and signal strength
Location Coordinates: Shows your current latitude and longitude
Dark Mode Optimized: Clean interface that works well in all lighting conditions

How to Use

Open the app and grant location permissions when prompted
Mount your device securely in your vehicle
Start driving and observe both your vehicle's speedometer and the GPS speed
Toggle between different speed units using the unit indicator
View your speed history in the graph at the bottom of the screen
Compare altitude changes as you drive through varying elevations

Technical Details: GPS Speed vs. Vehicle Speedometer

Vehicle Speedometer Accuracy

Most vehicle speedometers are designed to display a speed that is slightly higher (typically 5-10%) than your actual speed. This is intentional and serves several purposes:

Legal protection: Manufacturers avoid liability from drivers inadvertently speeding
Tire wear: As tires wear down, speedometer readings can change
Safety margin: Encourages drivers to drive slightly under the speed limit

GPS Speed Measurement

GPS speed is calculated by measuring the distance traveled between satellite pings and is generally more accurate than mechanical speedometers:

Accuracy: Typically within 0.1-0.2 km/h (0.06-0.12 mph) when good signal is available
No mechanical variables: Not affected by tire size, wear, or pressure
Signal-dependent: Requires good satellite visibility for optimal accuracy

Factors Affecting Accuracy

GPS signal quality: Accuracy decreases in tunnels, dense urban areas, or heavy tree cover
Device position: Best results when device has clear view of the sky
Update frequency: The app updates speed multiple times per second for smooth readings

Requirements

iOS 18.3 or later
iPhone or iPad with GPS capability
Location Services enabled

Privacy

This app uses location services only when the app is active. No location data is collected or transmitted to external servers. Location data is only used locally to calculate and display your speed and altitude.