diff --git a/Test_Cases/Test_Case3/readme b/Test_Cases/Test_Case3/readme
index abe2217..8f65104 100644
--- a/Test_Cases/Test_Case3/readme
+++ b/Test_Cases/Test_Case3/readme
@@ -11,7 +11,7 @@ This folder contains details for Test_Case3.
 7. Fragment Offset = 0 for now,
 8. Time To Live (TTL) = 40s, which is 28 in hex.
 9. Protocol = 6, which indicates TCP protocol is used.
-10. Header Checksum 
+10. Header Checksum = initially zero and then changed to the sum of 16 bit values of header + data.
 11. Source Address = 172.168.5.3, which is aca8 0503 in hex.
 12. Destination Address = 172.168.5.4, which is aca8 0504 in hex.
 13. Source Port = 5555, which is 15b3 in hex.