Bob,
Use the thumbwheel and roll to the gps readout screen. Downclick the thumbwheel, rotate wheel down - click wheel - rotate to SPEED GPS. Down click and rotate and click to the setting you want. Make sure use is YES. If you click wrong or go where you don't want to press either esc button on the top and you will back up to the last screen. learn to use those esc buttons! The warning at the bottom can be set at your choice of mph and can give an audio or vibration warning in the TX. I set mine for a mid course speed and it vibrates in my hand letting me know at what point on the straightaway I hit that speed. Good for checking prop acceleration or just set for desired op speed. love the radio but it is pricey. But realtime speeds helps prop and setup.
Mic