Properly compute variance when an offset is added

measure-analysis/measure-analysis.py

@@ -356,11 +356,12 @@ class MeasureSet:
             sum_prop = sum(prop)
 
             avg = sum(map(lambda x: abs(x[0] - self.middle)*x[1], enumerate_prop)) / sum_prop
+            avg_centered = sum(map(lambda x: x[0]*x[1], enumerate_prop)) / sum_prop
             var = 0
             for x, p in enumerate_prop:
                 var += p * x**2
             var /= sum_prop
-            var -= (avg + self.middle)**2
+            var -= avg_centered**2
 
             self.avg.append(avg)
             self.var.append(var)

measure-analysis/measures/measure-report.md

@@ -59,7 +59,7 @@ Min                           | Max                           | Avg
 Min         | Max        | Avg        | Var       
 ----------- | ---------- | ---------- | ----------
 **jitter**  | **jitter** | **jitter** | **jitter**
--100.0000us | 186.0000us | 39.1402us  | 152.1151us
+-100.0000us | 186.0000us | 39.1402us  | 252.7494us
 
 ![alt text](graphs/packet_jitterjitter.png "packet_jitter Graph")