Thanks Surfeditor,
Bigcodon,
I think you missed part of my post. I said that the numbers are the projected hieght of the tide (I say projected because wind can have a great effect on the tide height as well) above or below mean high water. Which, as you indicated, is the water depth used on all of our charts.
I was just going on to explain that you can use those numbers to figure what the current will be like in an area. As the difference between the two numbers increases, during a period of full or new moons, so does the current.