public void AddRange(IEnumerable <KeyValuePair <double, double> > items)
{
Power.AddRange(items);
double xmin = Power.Min(kvp => kvp.Key);
double xmax = Power.Max(kvp => kvp.Key);
double ymin = Power.Min(kvp => kvp.Value);
double ymax = Power.Max(kvp => kvp.Value);
double yavg = Power.Average(kvp => kvp.Value);
PowerAvg.Clear();
PowerAvg.Add(new KeyValuePair <double, double>(xmin, yavg));
PowerAvg.Add(new KeyValuePair <double, double>(xmax, yavg));
}