Top: schematic showing definition of angles used. Ω_inv is the longitude of ascending node measured in the invariable plane, with the reference direction chosen to be along the intersection between the sky and invariable planes. As the orbit normal precesses around the normal to the invariable plane, the planet’s inclination with respect to the invariable plane i_inv remains fixed, but the observed sky-plane inclination i_sky varies. Bottom: lower limit on ﹩{\dot{{\rm{\Omega }}}}_{{\rm{inv}}}﹩ from our measured ﹩\dot{b}﹩, for a range of planetary inclinations i_inv and angles between the invariable and sky planes I. White lines show contours of constant ﹩| {\dot{{\rm{\Omega }}}}_{{\rm{inv}}}| ﹩. The configuration shown in the top panel corresponds to a transiting planet system with low mutual inclinations, such that i_sky ∼ I ∼ 90^∘, i_inv ≲ 10^∘. In such a system, the typical lower limit on ﹩| {\dot{{\rm{\Omega }}}}_{{\rm{inv}}}| ﹩ based on our measured ﹩\dot{b}﹩ is an order of magnitude larger than the conservative limit of >0﹩\mathop{.}\limits^{{\unicode{x000b0}}}﹩5 yr⁻¹.