MISC 的 CPK计算，提取出来

Project.FLY.Misc/MISC/Enumerable.cs

@@ -76,13 +76,15 @@ namespace Misc
 
             double avg = source.Average(selector);
             double sigma3 = source.Sigma(selector) * 3;
-
+            return CPK(avg, sigma3, usl, lsl);
+        }
+        public static double CPK(double avg, double sigma3, double usl, double lsl)
+        {
             double CPKu = Math.Abs(usl - avg) / sigma3;
             double CPKl = Math.Abs(lsl - avg) / sigma3;
             double CPK = Math.Min(CPKu, CPKl);
             return CPK;
         }
-
         /// <summary>
         /// 获取CPK
         /// </summary>