I have a Garmin 301 that I wear on my wrist. I can display up to four data windows from a list of selections (eg. speed, heading, distance to mark, vmg). It cost $99 and is waterproof. I can easily "ping" the ends of the starting line if I want to get distance or time to either end but I do not use that except for big boat racing. It is very accurate and always with you as well and I highly recommend this device. Besides tactical uses, add a good radio to your person and you are in pretty good shape for serious safety situations.