At one time the legal limit for driving under the influence in California was .15, then it was reduce to .10 and now it resides at .08. Clearly the human body has not changed in it's reaction to alcohol over the years.
So, is there any agreement amongst nations as to what the legal limit should be? Not really, only Swaziland set their limit at .10, most are at .08 and many are lower like Poland at only .02. Really? I seems appropriate to mention that alcohol like most drugs effects each individual differently.
Those who work in the Sacramento District Attorney's Crime Lab and testify for the District Attorney generally testify that they believe that all people are "Impaired for the purpose of driving" at .08 and some people may be impaired below a .08.
California law presumes that drivers are NOT IMPAIRED if their blood alcohol concentration is .05 or lower.