Distance modulus uncertainties (top panel) and log(age) uncertainties σ_τ (bottom panel) as functions of the distance modulus. Lines show median values in 0. m 5 distance modulus bins. Colours are for datasets: dataset 1 – complete survey (red); dataset 2 – TGAS overlap (black); dataset 3 – TGAS overlap with TGAS parallaxes (blue); dataset 4 – TGAS parallaxes with EoM precisions (magenta); dataset 5 – UniDAM parallax with EoM precisions (orange). We show only distance modulus bins with at least five stars so as to reduce the noise. Therefore, the distance modulus range presented can differ for different datasets, especially for surveys with small overlap with TGAS The dotted black line shows F₁ (μ_d), the dashed black line shows F₂(μ_d) (as described in Sect. 4.1). Vertical grey lines and grey labels at the top panel mark borders between ranges A, B, and C (see Sect. 4.1 for details). Vertical grey line at the bottom plot marks maximum distance modulus for which the use of parallaxes gives at least 10% improvement in log(age) uncertainty (see Sect. 4.2). Middle panel: total number of stars in the survey (black) and the number of stars in overlap with TGAS (grey) as a function of distance modulus.