Address code review feedback: fix null handling and extract magic numbers

Co-authored-by: Pressacco <5507864+Pressacco@users.noreply.github.com>

Author: Copilot

Src/BlueDotBrigade.Weevil.Gui/Analysis/GraphViewModel.cs

@@ -30,6 +30,7 @@ public class GraphViewModel : INotifyPropertyChanged
 		private static readonly string FloatFormat = "0.000";
 		private static readonly int MaxSeriesCount = 4;
 		private static readonly string DefaultSeries2Suffix = " 2";
+		private static readonly int MetricsPrecision = 3;
 
 		// Y-Axis position options for each series
 		public static readonly string YAxisLeft = "Left";
@@ -862,35 +863,57 @@ private static ObservableCollection<SeriesMetrics> CalculateSeriesMetrics(
 
 					if (points.Any())
 					{
-						var values = points.Select(p => p.Value ?? 0.0).ToList();
+						// Filter out null values to avoid skewing statistics
+						var values = points
+							.Where(p => p.Value.HasValue)
+							.Select(p => p.Value.Value)
+							.ToList();
 						var timestamps = points.Select(p => p.DateTime).ToList();
 
-						var count = values.Count;
-						var min = values.Min();
-						var max = values.Max();
-						var mean = values.Average();
-						
-						// Calculate median
-						var sortedValues = values.OrderBy(v => v).ToList();
-						var mid = sortedValues.Count / 2;
-						var median = (sortedValues.Count % 2 == 0)
-							? (sortedValues[mid - 1] + sortedValues[mid]) / 2.0
-							: sortedValues[mid];
-						
-						var rangeStart = timestamps.Min();
-						var rangeEnd = timestamps.Max();
-						
-						var metrics = new SeriesMetrics(
-							lineSeries.Name ?? "Unknown",
-							count,
-							min,
-							max,
-							Math.Round(mean, 3),
-							Math.Round(median, 3),
-							rangeStart,
-							rangeEnd);
-						
-						metricsList.Add(metrics);
+						if (values.Any())
+						{
+							var count = values.Count;
+							var min = values.Min();
+							var max = values.Max();
+							var mean = values.Average();
+							
+							// Calculate median
+							var sortedValues = values.OrderBy(v => v).ToList();
+							var mid = sortedValues.Count / 2;
+							var median = (sortedValues.Count % 2 == 0)
+								? (sortedValues[mid - 1] + sortedValues[mid]) / 2.0
+								: sortedValues[mid];
+							
+							var rangeStart = timestamps.Min();
+							var rangeEnd = timestamps.Max();
+							
+							var metrics = new SeriesMetrics(
+								lineSeries.Name ?? "Unknown",
+								count,
+								min,
+								max,
+								Math.Round(mean, MetricsPrecision),
+								Math.Round(median, MetricsPrecision),
+								rangeStart,
+								rangeEnd);
+							
+							metricsList.Add(metrics);
+						}
+						else
+						{
+							// All values were null
+							var metrics = new SeriesMetrics(
+								lineSeries.Name ?? "Unknown",
+								0,
+								null,
+								null,
+								null,
+								null,
+								null,
+								null);
+							
+							metricsList.Add(metrics);
+						}
 					}
 					else
 					{

Src/BlueDotBrigade.Weevil.Gui/Analysis/SeriesMetrics.cs

@@ -7,6 +7,9 @@ namespace BlueDotBrigade.Weevil.Gui.Analysis
 	/// </summary>
 	public class SeriesMetrics
 	{
+		private const string NumericFormat = "0.000";
+		private const string DateTimeFormat = "yyyy-MM-dd HH:mm:ss";
+
 		public SeriesMetrics(
 			string seriesName,
 			int count,
@@ -39,11 +42,11 @@ public SeriesMetrics(
 		/// <summary>
 		/// Returns a formatted string representation suitable for display.
 		/// </summary>
-		public string MinFormatted => Min.HasValue ? Min.Value.ToString("0.000") : "N/A";
-		public string MaxFormatted => Max.HasValue ? Max.Value.ToString("0.000") : "N/A";
-		public string MeanFormatted => Mean.HasValue ? Mean.Value.ToString("0.000") : "N/A";
-		public string MedianFormatted => Median.HasValue ? Median.Value.ToString("0.000") : "N/A";
-		public string RangeStartFormatted => RangeStart.HasValue ? RangeStart.Value.ToString("yyyy-MM-dd HH:mm:ss") : "N/A";
-		public string RangeEndFormatted => RangeEnd.HasValue ? RangeEnd.Value.ToString("yyyy-MM-dd HH:mm:ss") : "N/A";
+		public string MinFormatted => Min.HasValue ? Min.Value.ToString(NumericFormat) : "N/A";
+		public string MaxFormatted => Max.HasValue ? Max.Value.ToString(NumericFormat) : "N/A";
+		public string MeanFormatted => Mean.HasValue ? Mean.Value.ToString(NumericFormat) : "N/A";
+		public string MedianFormatted => Median.HasValue ? Median.Value.ToString(NumericFormat) : "N/A";
+		public string RangeStartFormatted => RangeStart.HasValue ? RangeStart.Value.ToString(DateTimeFormat) : "N/A";
+		public string RangeEndFormatted => RangeEnd.HasValue ? RangeEnd.Value.ToString(DateTimeFormat) : "N/A";
 	}
 }