Absolute values of the glide 𝑔 introduced by a GW in positions (upper panel) and proper motions (lower panel) of the astrometric sources. The coloured bars show the range of values obtained in the five simulations for each frequency (see Sect. 4); for improved visibility the coloured lines connect the average statistics in the corresponding bars. The glide is computed from the spheroidal VSH coefficients of degree ℓ = 1 as described in Sect. 6 of Gaia Collaboration (2021). In our case, with negligible frame rotation in the data, the total glide is |𝑔| = (3/2)^1/2 R₁.