Probability density functions of differences between the Doppler velocity of Ca⁺H and Hϵ (red solid line), Ca⁺H and Hγ (red dashed line), Ca⁺IR and Hϵ (blue solid line), Ca⁺IR and Hγ (blue dashed line), Ca⁺H and Ca⁺IR (black solid line), and Hϵ and Hγ (black dashed line). For the functions b), the velocity differences were normalized to the measurement errors, σ. The black dotted line indicates the normal distribution with a standard deviation of 1.