diff --git a/src/00_about_arithmetics.sh b/src/00_about_arithmetics.sh
index a89a52e..746ce36 100644
--- a/src/00_about_arithmetics.sh
+++ b/src/00_about_arithmetics.sh
@@ -7,10 +7,13 @@ test_arithmetic_evaluation() {
 # shellcheck disable=SC2116
   output=$(echo 1+1)
 
-  assertEqual "$output" __
+  # `echo 1+1` is executed with the result given to `output`
+  # This is a demonstration of Bash command substitution.
+  assertEqual "$output" "1+1"
 
   output2=$((1+1))
 
-  assertEqual $output2 __
+  # Bash arithmetic, with "1+1" == 2
+  assertEqual $output2 2
 
 }