--- a/pkg/controllers/stretches.go	Fri Oct 25 16:12:43 2019 +0200
+++ b/pkg/controllers/stretches.go	Fri Oct 25 17:11:37 2019 +0200
@@ -10,6 +10,7 @@
 //
 // Author(s):
 //  * Sascha L. Teichmann <sascha.teichmann@intevation.de>
+//  * Sascha Wilde <wilde@intevation.de>
 
 package controllers
 
@@ -83,6 +84,45 @@
 	return false
 }
 
+func maxDuration(a time.Duration, b time.Duration) time.Duration {
+	if a > b {
+		return a
+	}
+	return b
+}
+
+func sumClassesTo(breaks []time.Duration, to int) time.Duration {
+	var result time.Duration
+	if to < 0 {
+		result = 0
+	}
+	for i := 0; i <= to; i++ {
+		result += breaks[i]
+	}
+	return result
+}
+
+func aggregateClasses(
+	new []time.Duration,
+	agg []time.Duration,
+) []time.Duration {
+	newAgg := make([]time.Duration, len(agg))
+
+	fmt.Printf("Old agg: %v\n", agg)
+	fmt.Printf("compwit: %v\n", new)
+	for i := 0; i < len(new)-1; i++ {
+		old_sum := sumClassesTo(agg, i)
+		new_sum := sumClassesTo(new, i)
+		newAgg[i] = maxDuration(new_sum, old_sum) - sumClassesTo(newAgg, i-1)
+	}
+	// adjust highest class so the sum of all classes in agg
+	// matches the original sum of all classes in new.
+	newAgg[len(new)-1] =
+		sumClassesTo(new, len(new)-1) - sumClassesTo(newAgg, len(new)-2)
+	fmt.Printf("New agg: %v\n", newAgg)
+	return newAgg
+}
+
 func loadFullStretchBottleneck(
 	ctx context.Context,
 	conn *sql.Conn,
@@ -311,12 +351,8 @@
 					if ldc == nil {
 						ldc, breaks = l, b
 					} else {
-						for i, v := range l {
-							ldc[i] += v
-						}
-						for i, v := range b {
-							breaks[i] += v
-						}
+						ldc = aggregateClasses(l, ldc)
+						breaks = aggregateClasses(b, breaks)
 					}
 				}
 
@@ -381,9 +417,6 @@
 		return
 	}
 
-	// Normalize to look like as we have only one bottleneck.
-	scale := 1 / float64(len(loaded))
-
 	empty := fmt.Sprintf("%.3f", 0.0)
 	for i := range record[1:] {
 		record[i+1] = empty
@@ -391,12 +424,6 @@
 
 	for _, r := range results {
 		// Round to full days
-		for i, v := range r.ldc {
-			r.ldc[i] = time.Duration(float64(v) * scale)
-		}
-		for i, v := range r.breaks {
-			r.breaks[i] = time.Duration(float64(v) * scale)
-		}
 		ldcRounded := common.RoundToFullDays(r.ldc)
 		rangesRounded := common.RoundToFullDays(r.breaks)
 
@@ -588,16 +615,12 @@
 					if ldc == nil {
 						ldc, breaks = l, b
 					} else {
-						for i, v := range l {
-							ldc[i] += v
-						}
-						for i, v := range b {
-							breaks[i] += v
-						}
+						ldc = aggregateClasses(l, ldc)
+						breaks = aggregateClasses(b, breaks)
 					}
 				}
 
-				duration := res.to.Sub(res.from) * time.Duration(len(loaded))
+				duration := res.to.Sub(res.from)
 
 				res.ldc = durationsToPercentage(duration, ldc)
 				res.breaks = durationsToPercentage(duration, breaks)