Bitcoin Universe · Model 04
The UTXO machine
A wallet does not hold a balance. It holds separate unspent outputs, each spent whole. Feed some into the machine and watch it make the payment, your change and the fee, to the exact satoshi.
What is happening
Payment
Your coins
Tick coins to put them in the machine. Each one is an unspent output of an earlier transaction, not a physical coin.
Reshape the wallet
Coin selection (wallet policy):
Privacy
Chosen inputs, displays and the fee
Coins (unspent outputs)
Simulated wallet
Coin size grows with the square root of its value; the displays show exact satoshis. All arithmetic is integer; a payment that would need more than the inputs is refused rather than allowed to go negative. Sizes assume P2WPKH inputs and outputs with 72-byte signatures. Split and consolidate are transactions to yourself and pay fees too.