If a driver is under DUI probation, what is the maximum legal blood alcohol concentration (BAC) that he or she may exhibit while operating a vehicle?

A California driver who is under DUI probation because of prior convictions may not have a BAC greater than 0.01% when operating a vehicle. Just one alcoholic drink will result in a BAC greater than 0.01%. [Blood Alcohol Concentration (BAC) Limit, Alcohol/Drugs and Driving is Dangerous, Alcohol and Drugs, California Driver Handbook]