Nerves of Steel/Fallout: New Vegas

Nerves of Steel is a perk in the Fallout 3 add-on Broken Steel and Fallout: New Vegas.

Broken Steel
It increases the regeneration rate of Action Points by 1 per 10 seconds. You naturally recover 4 AP every second, meaning you'll now restore 41 AP per 10 seconds instead of only 40. This amounts to a 2.5% (or so) increase in AP regeneration speed, and is hardly noticeable.

Fallout: New Vegas
The perk was retooled in Fallout: New Vegas to make it far more effective than the lackluster version in Fallout 3. According to the Fallout: New Vegas GECK, the perk now increases the regeneration rate of Action Points by 20% rather than a flat rate bonus. This means that you naturally recover 5 AP per second instead of 4.

Bugs

 * With patch 1.20.352, if you don't have a weapon equipped, this perk will not take effect.
 * In Fallout 3, PC users can alter the regeneration bonus associated with this perk by using the G.E.C.K. to edit the script DLC03APRegenScript. For users who do not know how to do so, a simple plugin can be found here.