Bitcoin & money learning · Retrospective
Why a transaction identifier needs an output index
Treat an identifier as a reference that must be specific enough to resolve.
Source foundation
Ordinary Bitcoin transactions spend earlier outputs and create new outputs. Bitcoin developer guide: transactions.
A worked example
A fictional transaction creates three outputs: 12,000, 18,000, and 24,000 satoshis. Labelling only the transaction leaves three possible destinations. In a zero-based list, output index 1 identifies the middle amount. A spreadsheet that loses that index cannot unambiguously track which output is spent.
Original hypothetical example. Amounts, people, events, and scenarios above are invented for learning; they are not historical observations or forecasts.
What to take from it
Good records preserve both the transaction reference and the particular output being discussed.
Try it on paper
Make a three-row paper ledger with an identifier and index column.
Keep the assumptions beside your answer. Check the result before applying the idea to a different situation.
Reading and limits
The linked source supports the foundation statement. The worked example and exercise are NAKAMOTO's educational analysis. This note does not establish current prices, product terms, investment suitability, or wallet compatibility.
Source reviewed 13 September 2026. For operational decisions, consult the current official documentation and the details of your own circumstances.