Transaction Hash Chain Signature: What Is Getting Signed? In Satoshi Nakamoto's diagram: 



I understand this diagram is dated--but please bear with me. I think I have missed a critical point of the diagram:

Question:
Let's assume that the three transactions depicted are #1, #2, and #3 from left to right. 

Is the Signature for Transaction #2 computed using Owner 1's Private Key and the Transaction data for Transaction #1 or is it computed using Owner 1's Private Key and the Transaction data for Transaction #2? 

Thank you.
Question: Let's assume that the three transactions depicted are #1, #2, and #3 from left to right.
Is the Signature for Transaction #2 computed using Owner 1's Private Key and the Transaction data for Transaction #1 or is it computed using Owner 1's Private Key and the Transaction data for Transaction #2?

The Signature for Transaction #2 is computed using Owner 1's Private Key and the Transaction data for Transaction #2.