I have to take exception Larry to your placing the S/L in last place. While it is true that GPS does give a very accurate speed, it is giving SOG, not boat speed through the water. By being able to see boat speed and compare it to GPS speed one can accurately figure the speed of any adverse, or beneficial current. Also, most of us use a speed averaging filter with a GPS unit, that would average speed over say 5 or 10 seconds to keep the reading relatively steady. By having a speedo that shows boat speed throuth the water the changes are instant and read out to 100ths of a knot. This helps me with sail trim.

So, each to his own in choosing and using instruments!

Rodd L