I have no idea because the clock on the computer, the clock on my cellphone and the two clocks in my bedroom all have a different time on them. Which one, if any, is correct?
We're very casual about time. We round up or down a quarter-hour when someone asks the time. We'll say that it's almost or just past an hour. "I'll be there in 15 minutes" might mean ten minutes or twenty minutes.
The court coordinator tells your client to be in court at 8:30 a.m. but the judge doesn't sit and call the docket until almost 9:00 a.m. The judge tells the parties in a case to be back in the courtroom at 1:30 p.m. but he doesn't return until almost 2:00 p.m.
Time is taken very seriously, though, at NASA where engines must be fired or shut down at a particular time in order for a spacecraft to get into or remain in a particular orbit. If mission control is off by a minute or two the astronauts could be lost forever or burned upon re-entry.
A watch, or a clock, is an instrument for measuring the passage of time. For most us of the accuracy of the instrument is relatively unimportant -- as long as we are where we are supposed to be within a reasonable tolerance, everyone is happy. We don't calibrate our watches and clocks on a regular basis because, in the end, it doesn't really matter all that much.
The point being, the degree of accuracy we require in our watches and clocks depends upon what is being measured and by whom. A houseful of clocks within a few minutes of each other is perfectly accepable -- a roomful of clocks within a few minutes of each other at NASA is not.
The same principle applies to the Intoxilyzer, or any other breath testing machine.
After all, just because I say my watch is accurate, does that make it so?