As a recent first time boat owner I have many questions. I have a speedometer on my dash (its the only gage there). I noticed on its maiden voyage on sunday that the gage didnt work. No big surprize its a 1965. I followed the black tubing all the way to the back of the boat and it ends in the water. The gage says "airguide". So my question is....... How the heck does it work? Perhaps I can make it perform its function if I understand the principle behind it. I am guessing water pressure but I have been surprized before. I understand that they arent accurate at all and most probably ignore them but its against my nature to see something broke and not at least take a half hearted attempt to fix something. Thanks for the inputs!