Model predictions for structure functions and their associated sample variances under two instrumental setups: XRISM/Resolve (assuming 1.5′ resolution elements) and Athena/X-IFU (assuming 5″ and 15″ resolution elements for high and low signal-to-noise ratios respectively). Left panel: predictions for a ∼15′×15′ contiguous mapping of the Coma cluster while the right panel shows the result for a single X-IFU pointing. A single Resolve pointing (3′ on a side) would be too small for a useful derivation of the structure function. The text gives further details on the input turbulent power spectrum and gas density model.