The HUD can update in any tick group, but TG_DuringPhysics is a good selection for two reasons. First, TG_DuringPhysics is acceptable because it doesn't directly interact with, or use data from, the game's physics simulation. Second, it is a good idea because there is no reason to force physics simulation to wait for the HUD to finish updating, nor is there a reason to force the HUD to wait for physics simulation to finish. Note that the HUD will be one frame behind the game, i.e. pointing at a target object this frame will not be reflected in the meter until next frame.