Might be PIC, but I feel like shouting “how low can you go!” over and over again. Every time I see one of these graphs I’m amazed by the swings. In this chart the recorded data went lower the charting software was built to accommodate. The deepest dip occurred on 12/20/2012 19:00:00, -0.905 meters (below chart datum). Curious thing about these charts, as I understand, they’re automated, but they don’t updated over weekends and holidays.