Push, Pull and the Instant Transfer - batch rails, instant rails, and who can be tricked

The chapter map: tanks, pipes, and valves that open only when both ends agree. This lesson is about the pipes between banks themselves: the old ones that carry water in tankers once a night, the new ones that carry it in seconds, and which end gets to open the tap.

Before you start. From Your Balance Is the Bank's Debt - deposits, reserves and the run: your balance is a promise your bank owes you, so paying someone at another bank means your bank owing you less and their bank owing them more, with the two banks squaring up between themselves. From Every Litre Leaves One Tank and Enters Another - double-entry, normal balances and the trial balance: each step is a pair of entries that sum to zero. The Hold That Is Not Money Yet - authorisation, capture, clearing, settlement and chargebacks helps but is not needed: a card payment is one kind of rail, and this lesson covers the others.