This is another example from cAlgo :

using System;
using cAlgo.API;
using cAlgo.API.Internals;
using cAlgo.API.Indicators;

namespace cAlgo.Indicators
{
[Indicator(IsOverlay = true, AccessRights = AccessRights.None)]
public class LinearRegressionChannel : Indicator
{
[Parameter(DefaultValue = 200)]
public int Bars { get; set; }

[Parameter(DefaultValue = "Yellow")]
public string Color { get; set; }

[Parameter(DefaultValue = 1.0)]
public double LineThickness { get; set; }

[Parameter("Center", DefaultValue = true)]
public bool ShowCenter { get; set; }

[Parameter("Channel", DefaultValue = true)]
public bool ShowChannel { get; set; }

[Parameter("Standard deviation", DefaultValue = true)]
public bool ShowDeviantion { get; set; }


private Colors color;

protected override void Initialize()
{
// Parse color from string, e.g. "Yellow", "Green", "Red". string must start with large letter, "Red" is valid, "red" - not.
if (!Enum.TryParse(Color, out color))
color = Colors.Yellow;
}

public override void Calculate(int index)
{
if (IsLastBar)
LinearRegression(MarketSeries.Close);
}

private void LinearRegression(DataSeries series)
{
// Linear regresion

double sum_x = 0, sum_x2 = 0, sum_y = 0, sum_xy = 0;

int start = series.Count - Bars;
int end = series.Count - 1;

for (int i = start; i <= end; i++)
{
sum_x += 1.0 * i;
sum_x2 += 1.0 * i * i;
sum_y += series[i];
sum_xy += series[i] * i;
}

double a = (Bars * sum_xy - sum_x * sum_y) / (Bars * sum_x2 - sum_x * sum_x);
double b = (sum_y - a * sum_x) / Bars;


// Calculate maximum and standard devaitions

double maxDeviation = 0;
double sumDevation = 0;

for (int i = start; i <= end; i++)
{
double price = a * i + b;
maxDeviation = Math.Max(Math.Abs(series[i] - price), maxDeviation);
sumDevation += Math.Pow(series[i] - price, 2.0);
}

double stdDeviation = Math.Sqrt(sumDevation / Bars);

// draw in future
end += 20;

double pr1 = a * start + b;
double pr2 = a * end + b;

if (ShowCenter)
{
ChartObjects.DrawLine("center", start, pr1, end, pr2, color, LineThickness, LineStyle.Lines);
}

if (ShowChannel)
{
ChartObjects.DrawLine("top", start, pr1 + maxDeviation, end, pr2 + maxDeviation, color, LineThickness, LineStyle.Solid);
ChartObjects.DrawLine("bottom", start, pr1 - maxDeviation, end, pr2 - maxDeviation, color, LineThickness, LineStyle.Solid);
}

if (ShowDeviantion)
{
ChartObjects.DrawLine("dev-top", start, pr1 + stdDeviation, end, pr2 + stdDeviation, color, LineThickness, LineStyle.DotsVeryRare);
ChartObjects.DrawLine("dev-bottom", start, pr1 - stdDeviation, end, pr2 - stdDeviation, color, LineThickness, LineStyle.DotsVeryRare);
}
}

}
}


thus the calculation should be fine but what about the plotting in Zorro?