Most people have experienced being pulled over by law enforcement officials and being asked to perform a Breathalyzer test. In the majority of cases, the person being tested will be able to prove that they are driving legally by having their blood alcohol concentration (BAC) measured in this way.
However, some people's BAC will be determined to be over the legal limit. This will happen if the Breathalyzer test displays BAC figures at 0.08% or higher. However, this evidence alone does not automatically prove that you were driving over the limit. This is because the Breathalyzer test may have been faulty, or other factors could have affected the result, for example, a health condition.