| CollapseModel | How much a rollup window collapses, derived rather than assumed. |
| Estimator | Projects what a site's history will cost, from measured constants rather than guesses. |
| FreeTierModel | Whether a projection fits inside what a provider gives away, and how big a site could. |
| Measurement | The shape of a site and the policy applied to it, as an estimate's input. |
| PriceTable | What one provider charges, and what it gives away. |
| Projection | What a measurement is projected to cost. |