A row in the middle

Here is the same machine with one row added between the tastes and the price.

The price still shows a question mark. The new row does not know what a wine costs yet. Its first job is simply to tell the four wine types apart.

Press any unit in the middle row to choose that wine. Its two tastes light up on the left. Exactly one middle unit reports 1, while the other three report 0.

Each middle unit has only two incoming wires. The plummy cabernet unit receives cabernet and plum. The apricotty cabernet unit receives cabernet and apricot. The other two work the same way.

This middle row has been built by hand for one narrow job, so we have included only the connections each unit uses.

The plummy cabernet unit asks whether cabernet and plum are both present. If only one arrives, it reports 0. If both arrive, it reports 1.

In logic, that is an AND: both conditions must be true at the same time.

Try the apricotty cabernet. Cabernet remains present, but plum disappears. The plummy cabernet unit goes back to 0, and the apricotty cabernet unit becomes 1.

The machine from the last chapter received two separate facts: cabernet and apricot. The middle row turns those facts into one new signal: apricotty cabernet.