Concept
An accuracy class is the ± band a TEA result carries, fixed by how mature and resolved the underlying work is rather than by how clean the arithmetic looks. Early factored estimates — front-end-loading stages FEL-1/2, equivalently AACE Class 5–4 — carry a wide band of order ±30–50%; the class, not the spreadsheet, sets how tight a range and how many significant figures the result can honestly carry.
What it is. Cost-estimating practice ties an estimate’s expected error to its maturity: the more defined the scope, equipment sizing, and pricing basis, the tighter the band. The same project is a different accuracy class at different stages of definition, even with identical arithmetic. A seed-stage TEA — factored, deterministic, proxy-grade — sits at the wide end of the ladder.
Two readings of the same maturity. The accuracy class is the output view — the ± band on the answer; the TEA Readiness Level is the input view — how resolved the model’s scope, data, and analysis are. They are the same axis read from opposite ends: a less-built model (a low TEA-RL) can only earn a wider class, and tightening the class means resolving the underlying build, not reworking the arithmetic. The class names the tolerance; the readiness level names what was built to deserve it.
The classes, roughly.
What it governs, and how it propagates. Precise arithmetic on a ±40% anchor still yields ±40% — the band is set by the worst load-bearing input, and capital estimates are typically asymmetric (overruns more common than under-runs, so the band skews high). Three downstream quantities read from this band: the contingency sized into total plant capital (larger for a less-resolved class); the resolution a reported headline number may honestly carry, since more is false precision; and the credible low/high ranges swept in a one-way sensitivity.