CPT practice has an admirable history on benchmarking accuracy of parameter values. A proposed Analytic CPT can serve as a benchmark for true values, independent of deployment-specific CPT features. This paper provides an introduction to CPT accuracy with reference to the proposed Ana-lytic CPT and with reference to CPT standard ISO 22476-1 and its application (accuracy) classes. ISO 22476-1 defines accuracy, where (1) cone resistance, sleeve friction and pore pressure are uncoupled from spatial position and (2) true values depend on permissible deployment-specific features. Uncertainty estimates are presented for favourable and adverse conditions. The adverse case illustrates difficulty in demonstrating compliance with the application classes of ISO 22476-1. Significant epistemic uncertainty is the principal reason for this situation, notably prediction models for transient temperature and meas-urement error. The uncertainty model provides what may be the first estimate that complies with ISO 22476-1 procedures. Actual accuracy is probably significantly better than calculated.