ch09: in seconds elapsed since Unix Epoch

ch09.asciidoc

@@ -43,7 +43,7 @@ One way to think about the blockchain is like layers in a geological formation,
 | 4 bytes | Version | A version number to track software/protocol upgrades
 | 32 bytes | Previous Block Hash | A reference to the hash of the previous (parent) block in the chain
 | 32 bytes | Merkle Root | A hash of the root of the merkle tree of this block's transactions
-| 4 bytes | Timestamp | The approximate creation time of this block (seconds from Unix Epoch)
+| 4 bytes | Timestamp | The approximate creation time of this block (in seconds elapsed since Unix Epoch)
 | 4 bytes | Difficulty Target | The Proof-of-Work algorithm difficulty target for this block
 | 4 bytes | Nonce | A counter used for the Proof-of-Work algorithm
 |=======