We invite contributions assessing dynamical and chemical models of the stratosphere (e.g. CTMs and CCMs). Existing and new observational platforms and instruments are challenging modellers to confront numerical simulations more quantitatively with the "real world". Questions arising are: Which observations are most useful? Which derived diagnostics are required? What statistical tools are most appropriate? Which metrics allow quantitative comparisons between models and observations? Is it possible to combine different measures or metrics? This session tries to encourage a broad cross-section of presentations relating to the above-mentioned theme (examples of observations, diagnostics, methods, techniques and metrics), fostering knowledge transfer and informed discussion.