Forging, hardening and tempering, then machine tools and precision.
Shape metal into tools — including the tools for shaping metal.
Needs first: Smelting: first metal (Materials)
Build machines that make machines — and break the accuracy ceiling.
Needs first: Blacksmithing, Steel and heat treatment (Materials)
Every guide, build, reference sheet and book reached from the steps above.
Iron is shaped by colour. Read the heat right and a bar of scrap becomes a chisel that holds an edge; read it wrong and it cracks, burns, or stays as soft as a nail.
Level 2Throw away two-thirds of the energy in a pile of wood and what is left is the only fuel that reaches the temperature of molten iron.
Level 3Four-figure logarithms and trigonometry, square roots by Newton's method, and the two instruments that did the world's arithmetic before electronics.
Level 3Density, stiffness, expansion and melting point for the materials the ladder makes, and what each number decides.
Level 3Turning the sciences into things that work: machines, structures, water in pipes and channels, heat through walls, and feedback control. Each result with what it lets you do and who first found it.
Continuous forced air — the component that decides whether you get metal or roasted rock.
A controlled hot spot you can hold a bar in — the hearth every other trade's tools come out of.
Turn wood into the fuel that reaches smelting heat — no kiln, no metal, just a stack, a cover and a week of attention.
A clay shaft that turns rock into iron — the first machine that makes every other machine possible.
The first machine tool — a sapling, a cord and a treadle, and the direct ancestor of everything in tier 3.
A few kilowatts, day and night, without eating — the first energy surplus large enough to support full-time specialists.
A whole building balanced on one oak post so it can be turned to face the wind — the first machine that let a settlement mill grain where there was no falling water.
Drawn overview sheets, each with its corrections printed under it. They orient; they are never the thing you identify from.
