Garmin makes motorcycle specific GPSs called the zumo line that include larger icons for gloved hands and a water/fuel resistant casing due to the possibility of the unit being exposed to the...
The best GPS should be of height quality and warrenty, easy to update map, with many up-to-date functions such as Bluetooth / IPOD /USB /SD /Detachable/MP4/MP3, etc, if including stereo with DVD...
actual mathematics is complicated, but basically by triangulating with multiple satellites by measuring signal time delay and solving a set of simultaneous equations to best convergence.
That would depend on what it is used for.
For navigation, I use the Garmin. It has been a very good unit and a reasonable price. You can check it out at www.garmin.com
However, for personal and/or...