You never can know the exact value of a physical or chemical dimension because several reasons: all the instruments have a certain sensibility (sensibility is the smallest variation of the dimension that the instrument can measure) that cannot be overcame.
According to the graph, the times for high tide would be 1 AM and 1 PM.
The low tides would be at 7 AM and 8 PM.
Good government, resources and trade with other places, and employment options.
