diff --git a/numass-main/src/main/groovy/inr/numass/scripts/Underflow.groovy b/numass-main/src/main/groovy/inr/numass/scripts/Underflow.groovy
index c54bbae2..af29f216 100644
--- a/numass-main/src/main/groovy/inr/numass/scripts/Underflow.groovy
+++ b/numass-main/src/main/groovy/inr/numass/scripts/Underflow.groovy
@@ -81,6 +81,6 @@ printPoint(data, [16200d, 16400d, 16800d, 17000d, 17200d])
 
 println()
 
-Table t = new UnderflowCorrection().fitAllPoints(data, 400, 700, 3100, 20);
+Table t = new UnderflowCorrection().fitAllPoints(data, 400, 650, 3100, 20);
 ColumnedDataWriter.writeDataSet(System.out, t, "underflow parameters")
 
diff --git a/numass-main/src/main/java/inr/numass/tasks/NumassPrepareTask.java b/numass-main/src/main/java/inr/numass/tasks/NumassPrepareTask.java
index b001206b..a1b4f630 100644
--- a/numass-main/src/main/java/inr/numass/tasks/NumassPrepareTask.java
+++ b/numass-main/src/main/java/inr/numass/tasks/NumassPrepareTask.java
@@ -10,8 +10,7 @@ import hep.dataforge.context.Context;
 import hep.dataforge.data.DataFilter;
 import hep.dataforge.data.DataNode;
 import hep.dataforge.data.DataTree;
-import hep.dataforge.description.DescriptorBuilder;
-import hep.dataforge.description.NodeDescriptor;
+import hep.dataforge.description.NodeDef;
 import hep.dataforge.meta.Meta;
 import hep.dataforge.meta.Template;
 import hep.dataforge.tables.Table;
@@ -27,6 +26,10 @@ import inr.numass.storage.NumassData;
  *
  * @author Alexander Nozik
  */
+@NodeDef(name = "prepare")
+@NodeDef(name = "monitor")
+@NodeDef(name = "merge")
+@NodeDef(name = "data")
 public class NumassPrepareTask extends AbstractTask<Table> {
 
     @Override
@@ -167,12 +170,12 @@ public class NumassPrepareTask extends AbstractTask<Table> {
         return "prepare";
     }
 
-    @Override
-    public NodeDescriptor getDescriptor() {
-        return new DescriptorBuilder(getName())
-                .addNode("prepare", PrepareDataAction.class)
-                .addNode("monitor", MonitorCorrectAction.class)
-                .addNode("merge", MergeDataAction.class)
-                .build();
-    }
+//    @Override
+//    public NodeDescriptor getDescriptor() {
+//        return new DescriptorBuilder(getName())
+//                .addNode("prepare", PrepareDataAction.class)
+//                .addNode("monitor", MonitorCorrectAction.class)
+//                .addNode("merge", MergeDataAction.class)
+//                .build();
+//    }
 }
diff --git a/numass-main/src/main/java/inr/numass/utils/PileUpSimulator.java b/numass-main/src/main/java/inr/numass/utils/PileUpSimulator.java
index 0916bdf7..3b1195d2 100644
--- a/numass-main/src/main/java/inr/numass/utils/PileUpSimulator.java
+++ b/numass-main/src/main/java/inr/numass/utils/PileUpSimulator.java
@@ -21,7 +21,6 @@ import static java.lang.Math.max;
  * @author <a href="mailto:altavir@gmail.com">Alexander Nozik</a>
  */
 public class PileUpSimulator {
-
     private final static double us = 1e-6;//microsecond
     private final double pointLength;
     private final RandomGenerator rnd;
diff --git a/numass-main/src/main/java/inr/numass/utils/UnderflowCorrection.java b/numass-main/src/main/java/inr/numass/utils/UnderflowCorrection.java
index 4bb914d5..b058a1df 100644
--- a/numass-main/src/main/java/inr/numass/utils/UnderflowCorrection.java
+++ b/numass-main/src/main/java/inr/numass/utils/UnderflowCorrection.java
@@ -26,6 +26,8 @@ import java.util.stream.Collectors;
  */
 public class UnderflowCorrection {
 
+    private final static int CUTOFF = -200;
+
     public double get(Logable log, Meta meta, NMPoint point) {
         if (point.getUset() >= meta.getDouble("underflow.threshold", 17000)) {
             if (meta.hasValue("underflow.function")) {
@@ -68,7 +70,7 @@ public class UnderflowCorrection {
             double sigma = fitRes[1];
 
             //builder.row(point.getUset(), a, sigma, (a * sigma * (Math.exp(xLow / sigma) - 1) - a*xLow) / norm + 1d);
-            builder.row(point.getUset(), a, sigma, a * sigma * (Math.exp(xLow / sigma)) / norm + 1d);
+            builder.row(point.getUset(), a, sigma, a * sigma * (Math.exp(xLow / sigma) - Math.exp(CUTOFF / sigma)) / norm + 1d);
         }
         return builder.build();
     }