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If accretion disc emission results from turbulent dissipation, thenaxisymmetric accretion theory must be used as a mean field theory: turbulentflows are at most axisymmetric only when suitably averaged. Spectralpredictions therefore have an intrinsic imprecision that must be quantified tointerpret the variability exhibited by a source observed at different epochs.We quantify contributions to the stochastic imprecision that come fromazimuthal and radial averaging and show that the imprecision is minimized for aparticular choice of radial averaging, which in turn, corresponds to an optimalspectral resolution of a telescope for a spatially unresolved source. If theoptimal spectral resolution is less than that of the telescope then the datacan be binned to compare to the theoretical prediction of minimum imprecision.Little stochastic variability is predicted at radii much larger than that atwhich the dominant eddy turnover time ($\sim$ orbit time) exceeds the timeinterval between observations; the epochs would then be sampling the samemember of the stochastic ensemble. We discuss the application of theseprinciples to protoplanetary discs for which there is presently a paucity ofmulti-epoch data but for which such data acquisition projects are underway.

Quantifying the Imprecision of Accretion Theory and Implications for Multi-Epoch Observations of Protoplanetary Discs