The proper way to read a nautical chart. Depths and dangers: The small numbers on a nautical chart are water depths at "Mean Lower Low Water," which is the average depth at the lower of each day's two low tides.Measurements at this level help boaters determine the closest underwater clearance possible for their boat. Reading the Tide Table. Now that you know why you need tide tables and where to get them, let’s move on to the most interesting part - learning to read them. First of all, it’s important to note that while tide charts and tables may be formatted differently, all the necessary information is still there. Swimmers, surfers, anglers, beachcombers, boaters, and many others will benefit from learning to read a tide table. Photo by Jon. How to read a tide table. Although the format and appearance of tide tables may differ, most will include the same three basic pieces of information: date, time, and tide height, organized in a grid-like structure.