diff --git a/doc/string/sum.rdoc b/doc/string/sum.rdoc
index 5de24e6402..125611411e 100644
--- a/doc/string/sum.rdoc
+++ b/doc/string/sum.rdoc
@@ -1,4 +1,4 @@
-Returns a basic +n+-bit checksum of the characters in +self+;
+Returns a basic +n+-bit {checksum}[https://en.wikipedia.org/wiki/Checksum] of the characters in +self+;
 the checksum is the sum of the binary value of each byte in +self+,
 modulo <tt>2**n - 1</tt>:
 
@@ -9,3 +9,5 @@ modulo <tt>2**n - 1</tt>:
   'こんにちは'.sum  # => 2582
 
 This is not a particularly strong checksum.
+
+Related: see {Querying}[rdoc-ref:String@Querying].