You don’t need an external GPS devices to use TDG, but we’d recommend that you do. TDG performs better with a little help as TDG will use your iPhone internal GPS receiver (unfortunately the maximum refresh rate is for the iPhone is 1Hz)

We suggest you purchase an external GPS unitm, operating at 5hz or greater, for more accurate session data and lap triggers – here are the TDG selected devices:

SkyPro GPS Receiver:

• Who: targeted at pilots, race car drivers, and other fast moving applications like a TDG Genius
• Why: up to 10 Hz refresh rate; 10 hours battery life; simple to use and quick set up
• Spec: see product manual
• Buy here: http://www.gps.co.uk/dual-xgps-160-skypro-gps-receiver/p-0-1431/

GLO™:

• Who: initially developed for GLO users of devices without internal built-in GPS, but it is now available for mobile devices.
• Why: 10 Hz refresh rate; 12 hours battery life; compact
• Spec: see product manual
• Buy here: http://www.gps.co.uk/garmin-glo-bluetooth-gps-for-mobile-devices/p-94-346-1482/

Bad Elf GPS for Lightning Connector:

• Who: rugged adventure seekers
• Why: up to 10 Hz refresh rate; 12 hours battery life; supports devices without built-in GPS
• Spec: Bad Elf Product Specification
• Buy here: http://www.gps.co.uk/bad-elf-gps-for-lightning-connector/p-94-346-1479/