Left: normalized distance PDF for V838 Mon (black line) which combines kinematic distance (green dashed line), Galactic latitude and spiral arm model (red dashed line), and source’s proper motion in Galactic longitude (blue solid line) and Galactic latitude (blue dashed line). The red arrow marks the distance range for possible arm associations. Right: normalized distance PDF for the various measurements of the V838 Mon parallax, including our VLBA astrometry, the Bayesian estimator, Gaia DR2, and the light echo.