diff --git a/src/main/c/main_taschenrechner.c b/src/main/c/main_taschenrechner.c
index 9158895..eb9dad3 100644
--- a/src/main/c/main_taschenrechner.c
+++ b/src/main/c/main_taschenrechner.c
@@ -44,6 +44,11 @@ double logarithmFunction(double x) {
     // Logarithm with base 10
     return log10(x);
 }
+
+double naturalLogarithmFunction(double x) {
+    // Natural logarithm (ln)
+    return log(x);
+}
  
 
 
diff --git a/src/main/c/taschenrechner.h b/src/main/c/taschenrechner.h
index d177979..071fba0 100644
--- a/src/main/c/taschenrechner.h
+++ b/src/main/c/taschenrechner.h
@@ -9,14 +9,19 @@ int multiply(int a, int b);
 
 int divide(int a, int b);
 
+// Trigonometric functions
 double sineFunction(double angle);
 
 double cosineFunction(double angle);
 
 double tangentFunction(double angle);
 
+//..
+// Logarithmic functions
 double logarithmFunction(double x);
 
+double naturalLogarithmFunction(double x);
+
 int mode(int userChoice);
 
 int displayMenu();