Box plot of variations in q and ϕ_q (value at the right side minus that at the left side) in different radial bins with a width of 4 kpc. Left: difference in q; right: difference in ϕ_q. For each bin, the red line means median, the box spans from Q1 (first quartile) to Q3 (third quartile), and the whiskers extend from the box to the smallest and largest values within 1.5 × interquartile range. The dashed line indicates zero difference.