hey, Ted, good formula. One I prefer, but GPS is SPEED OVER THE GROUND!!! Put it this way...I showed an increase of 10 mph on my Apache running with a 25 knot wind at my back and five knots of current going with me. Everyone on the boat went WHEW!!! Thats GPS for you. Turn the boat around in the same conditions and its all the other way. I'd prefer he used a pressure speedo. As a pilot, I file my IFR airspeed with ATC as indicated airspeed. I could return from Detroit in my plane showing 265 knots across the ground GPS but only 165 on the airspeed indicator for that altitude. The book says 175, so that what I file. All air traffic is travelling in the same 80-90 knot tail wind, so its relative. Good numbers TDan. Jerseyboygoesfast.