What does this equation mean?

which at the horizon itself scales as $\ell$ $c^6$/(4$G^2$$M^2$) — falling as the inverse square of the mass. For a processor of laboratory size $\ell$=1\,$\mathrm{cm}$ at the horizon of a black hole with the mass measured for the progenitors of the first LIGO gravitational-wave detection, around 30\,$M_\odot$ , this tidal stress is already about 1.1$\times$10^5\,$\mathrm{m\,s^{-2}}$ , on the order of ten thousand Earth gravities across a single centimeter — enough to disassemble ordinary hardware well before the horizon is reached [ 16 ] . For the Sagittarius A* mass used above, the same formula gives roughly 6$\times$10^{-6}\,$\mathrm{m\,s^{-2}}$ across the same centimeter: negligible, and consistent with the free-fall approximation actually holding at the horizon of a sufficiently large hole [ 14 ] . “Free fall is locally ordinary” is therefore not a universal statement about black holes; it is a statement whose validity is bounded, by real astrophysical data, to holes massive enough that the tidal term stays small over the processor’s own size — a condition satisfied at Sagittarius A*'s horizon and badly violated at a stellar-mass horizon of the kind LIGO has actually detected.