In Fallout 3, it increases AP by 1 point every 10 seconds. In New Vegas, It increases the regeneration rate of Action Points by 20%.
In Fallout 3, this perk may be less useful to those who have chosen the Grim Reaper's Sprint perk, as it fully restores Action Points upon killing an enemy in V.A.T.S. However, since some new enemies (such as super mutant overlords) in Broken Steel require multiple V.A.T.S. rounds to kill, playing on harder difficulty levels, and having few Action Points may make someone consider taking the script-edited version of Nerves of Steel.
In Fallout: New Vegas, this perk has become more useful, since Grim Reaper's Sprint only recovers 20 Action Points after killing an enemy in V.A.T.S.
PCXbox 360 It has been reported that the perk is non-functional in Fallout 3 on both the PC and Xbox 360 with the version 1.5 patch issued for Broken Steel, but this is inaccurate. While the perk does function, the increase in action point regeneration rate is extremely low (amounting to 1 additional AP per 10 seconds).[verified]
PC If you don't equip a weapon, this perk will not take effect (PC patch 1.20.352, but made irrelevant due to future patch).[verified]