Differences in parallaxes Δϖ_LT, Δϖ_LM,Δϖ_TM (from left to right) as a function of photometric parallax log ϖ_MWSC. The size of the circles is proportional to the number of individual parallaxes used for the computation of the averages. Vertical bars represent the mean errors of the differences computed as described in the text. The crosses in the left panel indicate vL2017 clusters with TGAS parallaxes for <17 probable MWSC members. The most distant cluster used in our comparison (data point at left edge in right panel) is the rich young cluster NGC 869 at about 2.3 kpc. The thick red lines indicate the mean differences and their mean errors.