The same model as the sliders-and-charts simulator, drawn as a water system instead of a spreadsheet: a pond of money circulating inside the village, a reservoir at the trade junction, and a sluice gate that throttles how fast money can drain out to the wider economy when the reservoir runs low.
Day 0
SlowFast
Watch the sluice gate at the junction: while the reservoir can cover what villagers want to spend abroad, it stays wide open. Push the reserve ratio down, or the demand up, and it visibly narrows — rationing outflow rather than letting the reservoir run dry. Flip on the backup main (external guarantor) and a dashed supply line from outside tops the reservoir up automatically instead of the gate ever closing.
Pond
the village's own money in circulation (τ supply)
Ocean
the much larger outside economy, priced in its own currency (F)
Reservoir
the trade reserve held at the junction (R)
Sluice gate
how much of the reserve can be released per day — the rationing rule of eq. (6)
Pressure gauge
how hard villagers are pushing to spend abroad relative to what the gate allows through
Backup main
the external guarantor (CFA-style backstop) topping up the reservoir
Recycling loop
demurrage: a small holding fee collected and paid back out as village spending, not destroyed
Current / whirlpool
local velocity — how fast money changes hands inside the village