Illustrations of the all-sky approximation to the parallax prior σ_ϖ,F90. Left: representative example of the linear fit in Eq. (15) of the logarithm of the parallax prior σ_ϖ,F90 as a function of galactic latitude b, for two magnitude ranges G = 9−10 (blue), and G = 19−20 (red). The small dependence on galactic longitude (the third term in Eq. (15)) has been subtracted leaving no systematic dependence on galactic longitude l, as shown by the different symbols (° for cosl> 0, + for cosl< 0). Middle: variations of the coefficients s₀, s₁, and s₂ with G magnitude, and polynomial fits according to Eqs. (16)–(18). Right: the prior σ_ϖ,F90 in Eq. (15) as a function of magnitude, for different latitudes (lowest to highest group: b = 0°, 30°, and 90°) and different longitudes (black solid l = 0°, red dashed 90°, blue dotted-dashed 180°).