I've had a few questions on this. The GPX Pro has an internal GPS antenna, so there is no need for a beacon at the side of the track.
Also, you can download your lap data to your laptop and do all kinds of lap time analysis with the very good XT racing software (free download from their website). Not to mention that you can get four channels of digital signals from your bike and one channel of analog for even more in-depth analysis.
If you are serious about improving your riding on the track, this can be a very effective tool for showing exactly what you and your bike are really doing at any point on the track. (Instead of what you think you are doing.)
