Basic floating-point arithmetic on the CPU follows the IEEE 754 standard and is therefore identical across platforms. However, GPUs relax the rules and don’t guarantee consistency. And CPUs differ in implementation of transcendantal functions like exp, sin, cos, pow. Generally as a game developer, these differences shouldn’t be significant, as UE4’s variable frame-rate model doesn’t ensure consistency of engine execution under identical input, and is designed to be generally numerically robust.