diff --git a/README.md b/README.md
index fa1058a..d801bc1 100644
--- a/README.md
+++ b/README.md
@@ -62,6 +62,7 @@ This object has 9 values
    * `xMaxFreq`|`xMinFreq`: character frequency.
    
 7. `dx`: true scale of x-axis.  
+   [Another width-extended canvas tag](#optional-settings) is recommended when `dx << 1`.  
    
 8. `dy`: true scale of y-axis.