Part V — Cost

What does the thing you have sized cost, over its life, and per unit of what it does?

Cost comes after sizing because it consumes sizing’s output. The fleet has already been chosen. This part is what it costs, and what that figure is and is not comparable with.

ch15 · Capex, opex and where the total stops splits what you pay once from what you pay every month, and notices which of the two got the meeting.

ch16 · Power first is what changes when the constraint is watts rather than money. It is the one place in the book where the sizing runs backwards and the rounding goes the other way.

ch17 · Unit economics turns a total into a number somebody outside the team can compare against something. It spends most of its time on the denominator, because nobody checks it.

ch18 · The five-year model is the seam between two models, where a distribution becomes a number in a document and the uncertainty quietly disappears.

The chains in this part are the deterministic half of ch01’s distinction: accounting identities and physics, with uncertain inputs and nothing in them that changes regime. Sampling the inputs is sufficient for those. Notice how much easier this part is than Part III. The ceilings are still there, and ch16 breaks one, but this part adds none of its own.