C# .NET method function to plot the tide changes.

TideChanges.cs

public static double PlotFromHighToLow(double highTide, double lowTide, double distance, double at)
{
    var halfAmplitude = Math.Abs(highTide - lowTide) / 2;
    var center = halfAmplitude + lowTide;

    var y = halfAmplitude * Math.Sin(((Math.PI / (distance)) * (at + (distance / 2)))) + center;
    return y;
}

public static double PlotFromLowToHide(double lowTide, double highTide, double distance, double at)
{
    return PlotFromHighToLow(highTide, lowTide, distance, at + distance);
}