diff --git a/numass-core/src/main/java/inr/numass/data/SpectrumDataAdapter.java b/numass-core/src/main/java/inr/numass/data/SpectrumDataAdapter.java
index 9c46ab1b..7beaa930 100644
--- a/numass-core/src/main/java/inr/numass/data/SpectrumDataAdapter.java
+++ b/numass-core/src/main/java/inr/numass/data/SpectrumDataAdapter.java
@@ -16,7 +16,6 @@
 package inr.numass.data;
 
 import hep.dataforge.exceptions.DataFormatException;
-import hep.dataforge.exceptions.NameNotFoundException;
 import hep.dataforge.meta.Meta;
 import hep.dataforge.meta.MetaBuilder;
 import hep.dataforge.tables.ValueMap;
@@ -25,6 +24,8 @@ import hep.dataforge.tables.XYAdapter;
 import hep.dataforge.values.Value;
 import hep.dataforge.values.Values;
 
+import java.util.Objects;
+
 /**
  * @author Darksnake
  */
@@ -59,7 +60,7 @@ public class SpectrumDataAdapter extends XYAdapter {
     }
 
     public double getTime(Values point) {
-        return this.getFrom(point, POINT_LENGTH_NAME, 1d).doubleValue();
+        return this.getComponent(point, POINT_LENGTH_NAME, 1d).doubleValue();
     }
 
     public Values buildSpectrumDataPoint(double x, long count, double t) {
@@ -79,30 +80,37 @@ public class SpectrumDataAdapter extends XYAdapter {
         return true;
     }
 
-    @Override
-    public Value getYerr(Values point) throws NameNotFoundException {
-        if (super.providesYError(point)) {
-            return Value.of(super.getYerr(point).doubleValue() / getTime(point));
-        } else {
-            double y = super.getY(point).doubleValue();
-            if (y < 0) {
-                throw new DataFormatException();
-            } else if (y == 0) {
-                //avoid infinite weights
-                return Value.of(1d / getTime(point));
-            } else {
-                return Value.of(Math.sqrt(y) / getTime(point));
-            }
-        }
-    }
-
     public long getCount(Values point) {
         return super.getY(point).numberValue().longValue();
     }
 
     @Override
-    public Value getY(Values point) {
-        return Value.of(super.getY(point).doubleValue() / getTime(point));
+    public Value getValue(Values point, String axis) {
+        if (Objects.equals(axis, XYAdapter.Y_AXIS)) {
+            return Value.of(getComponent(point, Y_VALUE_KEY).doubleValue() / getTime(point));
+        } else {
+            return super.getValue(point, axis);
+        }
     }
 
+    @Override
+    public Value getError(Values point, String axis) {
+        if (Objects.equals(axis, XYAdapter.Y_AXIS)) {
+            if (super.providesYError(point)) {
+                return Value.of(getComponent(point, Y_ERROR_KEY).doubleValue() / getTime(point));
+            } else {
+                double y = getComponent(point, Y_VALUE_KEY).doubleValue();
+                if (y < 0) {
+                    throw new DataFormatException();
+                } else if (y == 0) {
+                    //avoid infinite weights
+                    return Value.of(1d / getTime(point));
+                } else {
+                    return Value.of(Math.sqrt(y) / getTime(point));
+                }
+            }
+        } else {
+            return super.getError(point, axis);
+        }
+    }
 }
diff --git a/numass-main/src/main/groovy/inr/numass/scripts/models/TristanModel.groovy b/numass-main/src/main/groovy/inr/numass/scripts/models/TristanModel.groovy
index f620ea64..481eaa15 100644
--- a/numass-main/src/main/groovy/inr/numass/scripts/models/TristanModel.groovy
+++ b/numass-main/src/main/groovy/inr/numass/scripts/models/TristanModel.groovy
@@ -18,7 +18,7 @@ import inr.numass.data.SpectrumDataAdapter
 import inr.numass.data.SpectrumGenerator
 import inr.numass.models.NBkgSpectrum
 import inr.numass.models.NumassModelsKt
-import inr.numass.models.misc.GaussFunction
+import inr.numass.models.misc.Gauss
 import inr.numass.models.sterile.NumassBeta
 import inr.numass.utils.DataModelUtils
 
@@ -30,37 +30,45 @@ ctx.getPluginManager().load(NumassPlugin)
 
 new GrindShell(ctx).eval {
     def beta = new NumassBeta().getSpectrum(0)
-    def response = new GaussFunction(4.0)
+    def response = new Gauss(5.0)
     ParametricFunction spectrum = NumassModelsKt.convolute(beta, response)
 
     def model = new XYModel(Meta.empty(), new SpectrumDataAdapter(), new NBkgSpectrum(spectrum));
 
     ParamSet params = morph(ParamSet, [:], "params") {
         N(value: 1e+12, err: 30, lower: 0)
-        bkg(value: 1.0, err: 0.1)
+        bkg(value: 5.0, err: 0.1)
         E0(value: 18575.0, err: 0.1)
         mnu2(value: 0, err: 0.01)
         msterile2(value: 1000**2, err: 1)
         U2(value: 0.0, err: 1e-3)
-        X(value: 0.0, err: 0.01, lower: 0)
-        trap(value: 1.0, err: 0.05)
+        //X(value: 0.0, err: 0.01, lower: 0)
+        //trap(value: 1.0, err: 0.05)
         w(value: 150, err: 5)
+        //shift(value: 1, err: 1e-2)
+        tail(value: 1e-4, err: 1e-5)
     }
 
     SpectrumGenerator generator = new SpectrumGenerator(model, params, 12316);
 
     PlotHelper ph = plots
 
-    ph.plot((2000..19500).step(100).collectEntries {
-        [it, model.value(it, params)]
-    }, "spectrum").configure(showLine: true, showSymbol: false, showErrors: false, thickness: 3, color: "red")
+    ph.plot(data: (2000..19500).step(50).collectEntries { [it, model.value(it, params)] }, name: "spectrum")
+            .configure(showLine: true, showSymbol: false, showErrors: false, thickness: 2, connectionType: "spline", color: "red")
 
 
     Table data = generator.generateData(DataModelUtils.getUniformSpectrumConfiguration(10000, 19500, 1, 950));
 
     //params.setParValue("w", 151)
+    //params.setParValue("X", 0.01)
+    //params.setParValue("trap", 0.01)
+    //params.setParValue("mnu2", 4)
 
-    ph.plot(data).configure(color: "blue")
+    ph.plot(data: (2000..19500).step(50).collectEntries { [it, model.value(it, params)] }, name: "spectrum-mod")
+            .configure(showLine: true, showSymbol: false, showErrors: false, thickness: 2, connectionType: "spline", color: "green")
+
+    ph.plot(data: data, adapter: new SpectrumDataAdapter())
+            .configure(color: "blue")
 
     FitState state = new FitState(data, model, params);
 
diff --git a/numass-main/src/main/kotlin/inr/numass/models/misc/GaussFunction.kt b/numass-main/src/main/kotlin/inr/numass/models/misc/Gauss.kt
similarity index 92%
rename from numass-main/src/main/kotlin/inr/numass/models/misc/GaussFunction.kt
rename to numass-main/src/main/kotlin/inr/numass/models/misc/Gauss.kt
index 476eb58c..dddc1c6f 100644
--- a/numass-main/src/main/kotlin/inr/numass/models/misc/GaussFunction.kt
+++ b/numass-main/src/main/kotlin/inr/numass/models/misc/Gauss.kt
@@ -24,7 +24,7 @@ import java.lang.Math.*
 /**
  * @author Darksnake
  */
-class GaussFunction(private val cutoff: Double = 4.0) : AbstractParametricFunction(list), FunctionSupport {
+class Gauss(private val cutoff: Double = 4.0) : AbstractParametricFunction(*list), FunctionSupport {
 
     private fun getShift(pars: ValueProvider): Double {
         return pars.getDouble("shift", 0.0)
diff --git a/numass-main/src/main/kotlin/inr/numass/models/misc/TailFunctions.kt b/numass-main/src/main/kotlin/inr/numass/models/misc/TailFunctions.kt
new file mode 100644
index 00000000..95f98922
--- /dev/null
+++ b/numass-main/src/main/kotlin/inr/numass/models/misc/TailFunctions.kt
@@ -0,0 +1,41 @@
+package inr.numass.models.misc
+
+import hep.dataforge.stat.parametric.AbstractParametricFunction
+import hep.dataforge.values.Values
+
+class ConstantTail(private val defaultTail: Double = 0.0) : AbstractParametricFunction("tail") {
+    override fun derivValue(parName: String, x: Double, set: Values): Double {
+        if (parName == "tail" && x <= 0) {
+            return 1.0
+        } else {
+            return 0.0
+        }
+    }
+
+    override fun value(x: Double, set: Values): Double {
+        return if (x <= 0) {
+            set.getDouble("tail", defaultTail)
+        } else {
+            0.0
+        }
+    }
+
+    override fun providesDeriv(name: String): Boolean {
+        return true;
+    }
+}
+
+class exponentialTail : AbstractParametricFunction("tail") {
+    override fun derivValue(parName: String?, x: Double, set: Values?): Double {
+        TODO("not implemented") //To change body of created functions use File | Settings | File Templates.
+    }
+
+    override fun value(x: Double, set: Values?): Double {
+        TODO("not implemented") //To change body of created functions use File | Settings | File Templates.
+    }
+
+    override fun providesDeriv(name: String?): Boolean {
+        TODO("not implemented") //To change body of created functions use File | Settings | File Templates.
+    }
+
+}
\ No newline at end of file
diff --git a/numass-main/src/main/kotlin/inr/numass/models/sterile/NumassBeta.kt b/numass-main/src/main/kotlin/inr/numass/models/sterile/NumassBeta.kt
index 0b7ead19..c03c539f 100644
--- a/numass-main/src/main/kotlin/inr/numass/models/sterile/NumassBeta.kt
+++ b/numass-main/src/main/kotlin/inr/numass/models/sterile/NumassBeta.kt
@@ -204,7 +204,7 @@ class NumassBeta : AbstractParametricBiFunction(list) {
         return BetaSpectrum(fs);
     }
 
-    inner class BetaSpectrum(val fs: Double) : AbstractParametricFunction(list) {
+    inner class BetaSpectrum(val fs: Double) : AbstractParametricFunction(*list) {
 
         override fun providesDeriv(name: String): Boolean {
             return this@NumassBeta.providesDeriv(name)
diff --git a/numass-main/src/main/kotlin/inr/numass/models/sterile/SterileNeutrinoSpectrum.kt b/numass-main/src/main/kotlin/inr/numass/models/sterile/SterileNeutrinoSpectrum.kt
index c079725a..62335835 100644
--- a/numass-main/src/main/kotlin/inr/numass/models/sterile/SterileNeutrinoSpectrum.kt
+++ b/numass-main/src/main/kotlin/inr/numass/models/sterile/SterileNeutrinoSpectrum.kt
@@ -47,7 +47,7 @@ class SterileNeutrinoSpectrum @JvmOverloads constructor(
         configuration: Meta,
         val source: ParametricBiFunction = NumassBeta(),
         val transmission: NumassTransmission = NumassTransmission(context, configuration.getMetaOrEmpty("transmission")),
-        val resolution: ParametricBiFunction = NumassResolution(context, configuration.getMeta("resolution", Meta.empty()))) : AbstractParametricFunction(list) {
+        val resolution: ParametricBiFunction = NumassResolution(context, configuration.getMeta("resolution", Meta.empty()))) : AbstractParametricFunction(*list) {
 
 
     /**