diff --git a/demo/demo.qmd b/demo/demo.qmd
index 9ef81412..4d0b5f93 100644
--- a/demo/demo.qmd
+++ b/demo/demo.qmd
@@ -151,8 +151,10 @@ from your Markdown code.
 ## Math
 
 .sourceresult
-    If we try to calculate the **surface** of a circle of **radius 8**,
-    we'll find out it's **.multiply {.pow {8} to:{2}} by:{.pi}**
+    .var {radius} {8}
+
+    If we try to calculate the **surface** of a circle of **radius .radius**,
+    we'll find out it's **.multiply {.pow {.radius} to:{2}} by:{.pi}**
 
 ## Scripting {#scripting-basic}