diff --git a/lphy-base/src/main/java/lphy/base/evolution/coalescent/populationmodel/ExponentialPopulation.java b/lphy-base/src/main/java/lphy/base/evolution/coalescent/populationmodel/ExponentialPopulation.java
index 5796e555..97e5082c 100644
--- a/lphy-base/src/main/java/lphy/base/evolution/coalescent/populationmodel/ExponentialPopulation.java
+++ b/lphy-base/src/main/java/lphy/base/evolution/coalescent/populationmodel/ExponentialPopulation.java
@@ -135,6 +135,11 @@ public boolean isAnalytical() {
         return false; //use numerical method here
     }
 
+    @Override
+    public String toString() {
+        return "Exponential growth at a rate of " + GrowthRate +
+                ",\nwith an initial population size (N0) of " + N0;
+    }
 
     public static void main(String[] args) {
         double GrowthRate = 0.1;
diff --git a/lphy-studio/src/main/java/lphystudio/viewer/PopSizeFuncViewer.java b/lphy-studio/src/main/java/lphystudio/viewer/PopSizeFuncViewer.java
index 8007f9d4..c45834a0 100644
--- a/lphy-studio/src/main/java/lphystudio/viewer/PopSizeFuncViewer.java
+++ b/lphy-studio/src/main/java/lphystudio/viewer/PopSizeFuncViewer.java
@@ -24,9 +24,9 @@ public boolean match(Object value) {
     public JComponent getViewer(Object value) {
         //TODO create PopulationFunctionComponent((Value<PopulationFunction>) value)
         if (value instanceof PopulationFunction) {
-            return new JLabel("PopulationFunction TODO : " + value.toString());
+            return new JLabel(value.toString());
         }
-        return new JLabel("Value<PopulationFunction> TODO : " + ((Value<PopulationFunction>) value).value().toString());
+        return new JLabel(((Value<PopulationFunction>) value).value().toString());
     }
     @Override
     public String toString() {
diff --git a/lphy-studio/src/main/java/module-info.java b/lphy-studio/src/main/java/module-info.java
index f39184a6..c01a3d0e 100644
--- a/lphy-studio/src/main/java/module-info.java
+++ b/lphy-studio/src/main/java/module-info.java
@@ -30,10 +30,9 @@
     // ViewerRegister loads all Viewers
     uses lphystudio.app.graphicalmodelpanel.viewer.Viewer;
     // declare what service interface the provider intends to use
-    provides lphystudio.app.graphicalmodelpanel.viewer.Viewer with lphystudio.viewer.PopSizeFuncViewer;
     // the core uses hard core to register all internal Viewers,
     // but extensions need to declare what service interface the provider intends to use for new Viewers.
-//    provides lphystudio.app.graphicalmodelpanel.viewer.Viewer with lphystudio.app.graphicalmodelpanel.viewer.???Viewer, ...;
+    provides lphystudio.app.graphicalmodelpanel.viewer.Viewer with lphystudio.viewer.PopSizeFuncViewer;
 
     // Note: to adapt with the system not using Java module but using class path,
     // they need to be declared inside META-INF/services/lphystudio.app.graphicalmodelpanel.viewer.Viewer as well.
diff --git a/lphy-studio/src/main/resources/META-INF/services/lphystudio.app.graphicalmodelpanel.viewer.Viewer b/lphy-studio/src/main/resources/META-INF/services/lphystudio.app.graphicalmodelpanel.viewer.Viewer
index 7c4b7794..37748b92 100644
--- a/lphy-studio/src/main/resources/META-INF/services/lphystudio.app.graphicalmodelpanel.viewer.Viewer
+++ b/lphy-studio/src/main/resources/META-INF/services/lphystudio.app.graphicalmodelpanel.viewer.Viewer
@@ -7,4 +7,4 @@
 # but extensions need to declare what service interface the provider intends to use for new Viewers.
 # for example,  lphystudio.app.graphicalmodelpanel.viewer.???Viewer
 
-popsizefunc.lphystudio.viewer.PopSizeFuncViewer
\ No newline at end of file
+lphystudio.viewer.PopSizeFuncViewer
\ No newline at end of file