The National Oceanic and Atmospheric Administration (NOAA) measures tide levels at a few hundred locations in various United States territories. They take these measurements for several years. By analyzing the data, they create formulas that can predict tide levels in the future. These are called Reference Stations. NOAA also takes measurements at locations surrounding the Reference Stations to determine the time offset and level offset. These are called Subordinate Stations.

Water Current stations are completely independent of Tide Level stations. The equipment is used to gather the data is placed at various depths in areas where current is important to shipping and other national interests. San Francisco Bay, for example, has dozens of Water Current locations because of the strong current coming in and out of the bay. The formulas are calculated in a similar way, but it is completely independent of Tide Level data.

Tide Graph Pro offers several ways to choose a location. If you are connected to the internet, then you can use the map feature. Otherwise, you can search by name. If your GPS is enabled, you find locations near you. Below are 

	Tap the icon in the lower right corner.
	Choose Edit Locations
	Tap the (+) button.
	Choose any of the three options.
	On the "Use Map" screen, select Tides or Currents
	On the "Find Nearby Locations" screen, note that each station says Tide Level or Water Current
	On the "Search by Station Name" screen, note that each station says Tide Level or Water Current.