You set it up with tidal constants for your choice of standard port world-wide, and it then sits on your desktop, updating itself every minute from your computer clock, so it's live even when you're not connected to the net.
(And if you have any problems with Droggy's apparently-paranoid protection of public information--in the form of tidal constants--that he considers to be his and his alone, let me know...)
Thanks for the excellent info. Having a 6' draft for the first time ever is just a little scary.
Good sites. This weekend we took to exploring our chart plotter and discovered - to our amazement - that clicking on the 'T' box gives us the info. too. Isn't technology - including BBs wonderful?