Interactive model
The payment dial: turn a payment, watch the moorings respond
Set a payment size with the knob. The dial spends the largest berths first, marks which ones leave the dock, and shows the change that returns as a new berth. The units are illustrative and stand in for any amount.
Turn the knob
The interactive dial needs JavaScript. The reference table in section 02 shows the same rule without it.
Payment size, in units
50 units
Drag the knob, or press Tab to reach it and use the arrow keys. Page Up and Page Down move ten units at a time. Home sets zero and End sets one hundred.
- Berth A30 unitsSpent
- Berth B12 unitsUnspent, still moored
- Berth C25 unitsSpent
- Berth D8 unitsUnspent, still moored
- Berth E19 unitsUnspent, still moored
- Berth F6 unitsUnspent, still moored
- New berth5 unitsChange
The same rule, written out
The table below shows four payments worked by hand, with no knob required. It is the reference version of the dial, and it reads the same with or without JavaScript.
| Payment | Berths spent | Change |
|---|---|---|
| 25 units | A (30) | 5 units |
| 50 units | A (30), C (25) | 5 units |
| 75 units | A (30), C (25), E (19), B (12) | 11 units |
| 100 units | All six berths | None, exact match |
Reading the result
When the payment is covered, the berths listed as spent are used as inputs. Their total is the sum of the chosen values. The payment takes what it needs, and the rest returns as change. A berth that is not spent stays moored and remains unspent, available for a later payment.
If the payment equals the total of the chosen berths exactly, there is no change, and no new berth appears. A real transaction would also leave some of its inputs as a fee, which this dial leaves out.
What the dial leaves out
The dial uses one rule, largest first, to keep the model visible. It ignores fee rates, the cost of carrying extra inputs, privacy, and the order in which outputs were created. Those are the reasons real wallets work harder. Treat the dial as a picture of the shape of the problem, not as a guide to any particular wallet.
Not financial, legal, or medical advice. The dial is a teaching model. It makes no recommendation about payments, holdings, or any amount you should use.