The blue horizontally striped histograms show the “stochastic” noise added to Gaia measurements in the computation of a stochastic solution. The green diagonally striped ones represent the stochastic noise plus the offset of the mean photocentre position with respect to the centre of the star. The three panels show results for three different sets of parameters of the Markov chain. The vertical dashed line corresponds to the standard deviation σ_P in the photocentre displacement.