A card batch and a USDC transfer do not close on the same clock
How a Seosan counter can tell a card-batch cutoff from a confirmed USDC payment on Solana, using the fields the reading room prints.
At a dried-seafood stall in Unsan-myeon the card terminal still has a habit. Sales pile up through the afternoon, and the amount the bookkeeper trusts is the one that survives the acquirer’s batch, often overnight. A USDC payment on Solana behaves differently. Once the cluster confirms the transfer, the token amount is visible against the receiving address, and the fee has already been paid in SOL, not deducted from the dollar-pegged coin as a card scheme fee.
Two clocks on one counter
The card clock is the batch. Staff learn its cutoff because a sale after that time lands in the next day’s deposit. The stablecoin clock is the confirmation. In the reading room we treat the payment as ready to write down when a signature, a slot, a fee in lamports, and a token amount can all be read from the public record. We do not ask the stall to pretend those two clocks are one clock.
That difference is why a Thursday USDC receipt can sit in the book before the Wednesday card sales have cleared. The bookkeeper who tries to force both into the card column will mis-state the day. The four lines we dictate on a shop visit keep the stablecoin receipt in its own column: payer reference, signature, token amount, and the KRW figure the shop chose for that day.
What the fee is, and what it is not
The network fee on Solana is denominated in lamports of SOL. One SOL is one billion lamports. The fee is the cost of the transaction, not a percentage of the USDC. A card fee often feels like a slice of the sale. A Solana fee feels, on the printed table, like a small separate line that the payer’s wallet spent in SOL so the stablecoin could move.
The monthly sheet on shelf A records the fee range the director observed for ordinary token transfers, written as lamports and as a SOL decimal. It is a teaching sheet, refreshed from public figures, not a quote a shop can hold Mentis Junction to next month. Fees move. The sheet is dated in the corner for that reason.
How to explain it at the stall
Staff do better with one spoken sentence than with a diagram. The sentence we practise is: the dollar-pegged amount is the USDC, the confirmation is the signature, and the small extra spent to send it was SOL. Customers who already hold the coin usually recognise that split. Customers who do not are pointed back to a card or cash sale, which the stall still takes.
The seminar’s first sitting uses a blank card receipt beside a redacted public confirmation so the two clocks stay visible. If you only have a weekday, shelf B has three merchant notes from South Chungcheong that use the same split in ordinary language.
The October seminar spends its first sitting on this comparison, with the month’s fee table on the table.