Vertical component g_Z of self-gravity of a homogeneous disc computed from Eq. (14) compared with Paczynski’s formula versus the radius for Z = h (i.e., at the top of the disc). The disc parameters are a_in/a_out = 0.05, mass density ρ = 1, and semi-thickness h = 0.1a_out (model 1 in Table 1). When the radial extent of the disc increases, g_z tends to Paczynski’s formula, as indicated by the arrows, but edge effects are still present.