I've just looked at the gpsss site, they say that at the moment the navi
is the only unit that measures doppler, so for record attempts it's the only one acceptable. Here's what they say about it.
quote:
Some features of Navi GT11 / Amaryllo Triptracker:
* High accuracy GPS-Doppler speed measurement. 5*10 second average speed accurate to within 0.02 knots (95% confidence)
* 10 second max average speed displayed on screen with support for multiple speed attempts (with firmware 0727a and above)
* Automatic GPS data identification, including sailor''s name and the serial number of the GPS used
* Advanced Data Logger functions with ON-FIX and ON-SPEED recording
* TWO independent data loggers (SD card and Data Logger flash memory) for maximum reliability
* Support for SD card up to 2GB (small cards work fine and save battery power)
* Fast GPS data transfer and backup to SD card and external computers
* Store multiple tracks (surfing days) on the SD card (nice for on holiday).
* Re-charging capability in a car on a beach.