NanSea - Hate to tell you but Lat Lon is referenced to several different Datums (reference points). The earth isn't round, and the science of cartography (mapping) and the advent of GPS are pushing the need for better Datum's. Look closely at your nautical chart, you will see what datum was used. The differences are minor, if someone gives you lat/lon for large structure (cholera banks, 17, ) you'll never know the difference. GPS numbers have only become more transferable since SA was turned off, before that LORAN was much better (40-50 ft) vs. 50-100 yards. WAAS and DGPS are great, however, the governments own data base of wrecks (AWOIS) is referenced to the North American 1927 datum. Your GPS is not !! The conversion is different for various points on the globe. Check out Maptech S/W and others, they will convert the numbers for you. The offset is relatively small, but if you're into wreck fishing, and not merely trying to get on the wreck, but hit its sweet spot, you need all the help you can get. Good Luck.