Coding classes in Pembrokeshire

The learner models the sea as a smooth wave that peaks every 12.42 hours, the usual gap between high tides. Each minute the program checks three things. If the sea is above the pond, the gates are open and the pond rises with it. If the pond is at least 0.6 metres above the sea, the wheels can turn, so water leaves at a steady 2 cubic metres a second and the pond drops. Otherwise nothing happens. Every figure here, the pond size, the flow, the minimum drop, is our own invention, and the real Carew mill was, according to the record, only partly tidal.

Bigger tides fill the pond higher and drop the sea lower, so the mill works longer. With a pond three times the size, the same tides give 7.0, 8.2 and 9.0 hours. Next the learner prints when each grinding spell begins. Setting high water at midnight on the first day, the spells start at 01:35 and 14:00, then 02:25 and 14:50, then 03:16 and 15:41. Each day the work begins about 50 minutes later, because two tides take close to 24 hours 50 minutes. A miller's timetable crept around the clock through every month.

Two lessons about simulation come for free. Run the loop in one-hour steps and the big-tide answer becomes 8.0 hours, not 7.8, because each step assumes nothing changes for sixty minutes. Shrink the step and the answer settles. And drop the check that makes the gates one-way, so water can flow back out as the tide falls, and the pond simply follows the sea down: the mill never grinds at all. One missing condition wrecks the whole model, which is exactly why the gates mattered in 1615.

Hunting for the rule a program has forgotten is a skill a Pembrokeshire teenager gains by coding through 2026. The longer argument is in why teenagers should still learn to code in 2026.