Left: dark lines: radial forces K_R of the BGM at several z above the galactic plane (0.5, 1, 2, and 3 kpc, bottom to top). Thin green lines: K_R recovered from a Jeans equation in the case of a thick disc. Thin red lines: the case of a thin disc. Right: relative errors on the recovered radial force K_R versus R at various z (0.5, 1, 2, and 3 kpc; resp. green, black, red, and blue lines) for thin disc DF (dotted lines) and thick disc DF (continuous lines).