diff --git a/src/main/java/de/neemann/digital/core/ObservableValue.java b/src/main/java/de/neemann/digital/core/ObservableValue.java
index 5ed81d2c2..e5eeff499 100644
--- a/src/main/java/de/neemann/digital/core/ObservableValue.java
+++ b/src/main/java/de/neemann/digital/core/ObservableValue.java
@@ -22,8 +22,9 @@ public class ObservableValue extends Value {
         observers = new ArrayList<>();
     }
 
-    public void addObserver(Observer observer) {
+    public ObservableValue addObserver(Observer observer) {
         observers.add(observer);
+        return this;
     }
 
     public void removeObserver(Observer observer) {
diff --git a/src/main/java/de/neemann/digital/core/arithmetic/Add.java b/src/main/java/de/neemann/digital/core/arithmetic/Add.java
index 9f5ee05c0..3731aa73b 100644
--- a/src/main/java/de/neemann/digital/core/arithmetic/Add.java
+++ b/src/main/java/de/neemann/digital/core/arithmetic/Add.java
@@ -53,12 +53,9 @@ public class Add extends Node implements Part {
 
     @Override
     public void setInputs(ObservableValue... inputs) throws BitsException {
-        a = inputs[0];
-        a.addObserver(this);
-        b = inputs[1];
-        b.addObserver(this);
-        c_in = inputs[2];
-        c_in.addObserver(this);
+        a = inputs[0].addObserver(this);
+        b = inputs[1].addObserver(this);
+        c_in = inputs[2].addObserver(this);
 
         if (a.getBits() != bits)
             throw new BitsException("wrongBitCount", a);
diff --git a/src/main/java/de/neemann/digital/core/arithmetic/Mul.java b/src/main/java/de/neemann/digital/core/arithmetic/Mul.java
index 432fa7292..6a967e17d 100644
--- a/src/main/java/de/neemann/digital/core/arithmetic/Mul.java
+++ b/src/main/java/de/neemann/digital/core/arithmetic/Mul.java
@@ -39,10 +39,8 @@ public class Mul extends Node implements Part {
 
     @Override
     public void setInputs(ObservableValue... inputs) throws NodeException {
-        a = inputs[0];
-        a.addObserver(this);
-        b = inputs[1];
-        b.addObserver(this);
+        a = inputs[0].addObserver(this);
+        b = inputs[1].addObserver(this);
     }
 
     @Override
diff --git a/src/main/java/de/neemann/digital/core/basic/Not.java b/src/main/java/de/neemann/digital/core/basic/Not.java
index 02b745863..e078e7cc6 100644
--- a/src/main/java/de/neemann/digital/core/basic/Not.java
+++ b/src/main/java/de/neemann/digital/core/basic/Not.java
@@ -38,8 +38,7 @@ public class Not extends Node implements Part {
 
     @Override
     public void setInputs(ObservableValue... inputs) throws NodeException {
-        input = inputs[0];
-        input.addObserver(this);
+        input = inputs[0].addObserver(this);
     }
 
     @Override
diff --git a/src/main/java/de/neemann/digital/core/basic/XOr.java b/src/main/java/de/neemann/digital/core/basic/XOr.java
index d19799fcd..515c51407 100644
--- a/src/main/java/de/neemann/digital/core/basic/XOr.java
+++ b/src/main/java/de/neemann/digital/core/basic/XOr.java
@@ -38,10 +38,8 @@ public class XOr extends Node implements Part {
 
     @Override
     public void setInputs(ObservableValue... inputs) throws BitsException {
-        a = inputs[0];
-        a.addObserver(this);
-        b = inputs[1];
-        b.addObserver(this);
+        a = inputs[0].addObserver(this);
+        b = inputs[1].addObserver(this);
 
         if (a.getBits() != bits)
             throw new BitsException("wrongBitCount", a);
diff --git a/src/main/java/de/neemann/digital/core/flipflops/D_FF.java b/src/main/java/de/neemann/digital/core/flipflops/D_FF.java
index bcb0d90f8..29309bc3b 100644
--- a/src/main/java/de/neemann/digital/core/flipflops/D_FF.java
+++ b/src/main/java/de/neemann/digital/core/flipflops/D_FF.java
@@ -45,10 +45,8 @@ public class D_FF extends Node implements Part {
 
     @Override
     public void setInputs(ObservableValue... inputs) throws BitsException {
-        dVal = inputs[0];
-        dVal.addObserver(this);
-        clockVal = inputs[1];
-        clockVal.addObserver(this);
+        dVal = inputs[0].addObserver(this);
+        clockVal = inputs[1].addObserver(this);
 
         if (dVal.getBits() != bits)
             throw new BitsException("wrongBitCount", dVal);
diff --git a/src/main/java/de/neemann/digital/core/flipflops/JK_FF.java b/src/main/java/de/neemann/digital/core/flipflops/JK_FF.java
index 9b7c082c4..ae0ae0daa 100644
--- a/src/main/java/de/neemann/digital/core/flipflops/JK_FF.java
+++ b/src/main/java/de/neemann/digital/core/flipflops/JK_FF.java
@@ -49,12 +49,9 @@ public class JK_FF extends Node implements Part {
 
     @Override
     public void setInputs(ObservableValue... inputs) throws BitsException {
-        jVal = inputs[0];
-        jVal.addObserver(this);
-        clockVal = inputs[1];
-        clockVal.addObserver(this);
-        kVal = inputs[2];
-        kVal.addObserver(this);
+        jVal = inputs[0].addObserver(this);
+        clockVal = inputs[1].addObserver(this);
+        kVal = inputs[2].addObserver(this);
 
         if (jVal.getBits() != 1)
             throw new BitsException("wrongBitCount", jVal);
diff --git a/src/main/java/de/neemann/digital/core/flipflops/RS_FF.java b/src/main/java/de/neemann/digital/core/flipflops/RS_FF.java
index 68ff764a2..b3a936c5a 100644
--- a/src/main/java/de/neemann/digital/core/flipflops/RS_FF.java
+++ b/src/main/java/de/neemann/digital/core/flipflops/RS_FF.java
@@ -48,12 +48,9 @@ public class RS_FF extends Node implements Part {
 
     @Override
     public void setInputs(ObservableValue... inputs) throws BitsException {
-        jVal = inputs[0];
-        jVal.addObserver(this);
-        clockVal = inputs[1];
-        clockVal.addObserver(this);
-        kVal = inputs[2];
-        kVal.addObserver(this);
+        jVal = inputs[0].addObserver(this);
+        clockVal = inputs[1].addObserver(this);
+        kVal = inputs[2].addObserver(this);
 
         if (jVal.getBits() != 1)
             throw new BitsException("wrongBitCount", jVal);
diff --git a/src/main/java/de/neemann/digital/core/flipflops/T_FF.java b/src/main/java/de/neemann/digital/core/flipflops/T_FF.java
index db8fa8c46..686da634f 100644
--- a/src/main/java/de/neemann/digital/core/flipflops/T_FF.java
+++ b/src/main/java/de/neemann/digital/core/flipflops/T_FF.java
@@ -42,8 +42,7 @@ public class T_FF extends Node implements Part {
 
     @Override
     public void setInputs(ObservableValue... inputs) throws BitsException {
-        clockVal = inputs[0];
-        clockVal.addObserver(this);
+        clockVal = inputs[0].addObserver(this);
 
         if (clockVal.getBits() != 1)
             throw new BitsException("carryIsABit", clockVal);
diff --git a/src/main/java/de/neemann/digital/core/wiring/Delay.java b/src/main/java/de/neemann/digital/core/wiring/Delay.java
index ca653538b..9a3a4c306 100644
--- a/src/main/java/de/neemann/digital/core/wiring/Delay.java
+++ b/src/main/java/de/neemann/digital/core/wiring/Delay.java
@@ -42,8 +42,7 @@ public class Delay extends Node implements Part {
 
     @Override
     public void setInputs(ObservableValue... inputs) throws NodeException {
-        input = inputs[0];
-        input.addObserver(this);
+        input = inputs[0].addObserver(this);
 
         if (input.getBits() != bits)
             throw new BitsException("wrongBitCountInDelay", input, output);