diff --git a/Test_Cases/Test_Case1/readme b/Test_Cases/Test_Case1/readme
index 93a2bea..1c2f1de 100644
--- a/Test_Cases/Test_Case1/readme
+++ b/Test_Cases/Test_Case1/readme
@@ -11,7 +11,7 @@ The values for the header fields are:
 7. Fragment Offset = For now, there is no fragment offset so, this value is set to 0.
 8. TTL = 40s, which is 28 in hex.
 9. Protocol = 6, which indicates TCP.
-10. Header Checksum = initially zero and then changed to the sum of 16 bit values of header + data.
+10. Header Checksum = initially zero and then changed to the 1's complement of the sum of 16 bit values of IP header + data.
 11. Source IP        = 200.204.10.12, which is c8cc 0a0c in hex
 12. Destination IP   = 200.204.10.14, which is c8cc 0a0e in hex
 13. Source Port      = 1234, which is 04D2 in hex,