diff --git a/src/checks/level1/README-qstring-left.md b/src/checks/level1/README-qstring-left.md
index 5e60728..b4b53a9 100644
--- a/src/checks/level1/README-qstring-left.md
+++ b/src/checks/level1/README-qstring-left.md
@@ -1,4 +1,9 @@
 # qstring-left
 
-Finds places where you're using `QString::left(0)` instead of `QString::at(0)`.
-The later form is cheaper.
+Finds places where you're using `QString::left(1)` instead of `QString::at(0)`.
+The later form is cheaper, as it doesn't deep-copy the string.
+
+There's however another difference between the two: `left(1)` will return an empty
+string if the string is empty, while `QString::at(0)` will assert. So be sure
+that the string can't be empty, or add a `if (!str.isEmpty()` guard, which is still
+faster than calling `left()` for the cases which deep-copy.