Expanded clock guides on model fitting and personal uncertainty

Expanded two existing aging-clock guides with source-linked explanations of model fitting, calibration and uncertainty.

How epigenetic clocks work now explains how sites and weights are fitted together, notes nonlinear models, and distinguishes held-out group accuracy from personal accuracy. The limitations of aging clocks explains why a reported median error is not a personal margin or a threshold for meaningful change. It also separates age-prediction accuracy from links with later health outcomes. The additions include primary references, relevant commercial-interest disclosures and the original multi-tissue clock’s erratum.

Readers should not interpret a model-development accuracy figure as a guarantee about their own result.

The additions explain existing limitations; they do not change test ratings or establish that a score change means improved health. The pages disclose AI assistance and separate AI review, not external expert validation.