Rotation velocity at R_max = 3′ vs. kinematic position angle recovered from the tests on mock catalogues reproducing the characteristics of the FORS2 data set and simulating a linear rotation model. Gray circles represent input values at n = 1.5, 1.0, 0.75, 0.5, 0.25, 0.; colored circles, squares, and triangles represent recovered values at different simulated kinematic PA; colors from blue to brown represent decreasing values of n, while the error bars are the 99% confidence interval (C.I.); in black the observed value from our data set with error bars at 68% C.I.