var plot = AvaPlot.Plot;
var color = Colors.Cyan;

var vLine = plot.Add.VerticalLine(1000, 1, color, LinePattern.Dashed);
vLine.LabelFontColor = Color.FromARGB(0xC0000000);
vLine.LabelBorderColor = color;
vLine.LabelBackgroundColor = Colors.Transparent;
vLine.LabelText = $"{Math.Round(1000f, 3)}Hz"; // Label the line with its position
vLine.LabelRotation = -90;
vLine.LabelAlignment = Alignment.MiddleRight;
vLine.LabelOffsetX = -20;
vLine.LabelOffsetY = -250;