Sequential posterior power-spectrum (left panel) and 1-pt distribution (right panel) of inferred primordial fluctuations measured during the burn-in of the Markov chain with an LPT model. The colour gradient indicates the step number in the chain from zero (random initial condition of small amplitude) to 6783 for which the chain is manifestly stable according to this metric. Top panels: power spectrum and 1-pt distributions measured a posteriori from the samples, while lower panels: ratio of these quantities to the expected prior values. Thick dashed lines represent the fiducial prior values. The thin (black respectively) grey dotted line indicates the Gaussian 1σ limit (2σ respectively) in the lower left panel. These results show no sign of any residual systematic artefacts, indicating a healthy burn-in behaviour of the chain.