Ask an engineer and he may be happy to explain the theory behind the little magic black box, whose digital readout is, standing alone, sufficient to put a person in prison. When the Breathalyzer 5000 was accepted as proof of drunk driving, it became a fixture of the law. There aren’t many bank robbers, but there are a ton of drunk drivers. We know because the box says so.

In time, the magic science of the box became the subject of scrutiny. Experts questioned its accuracy, both internally and theoretically. After all, it purported to measure the alcohol in a person’s breath, while the salient information was the alcohol in a person’s blood. It gave a number, which conclusively proved a crime notwithstanding the absence of evidence that the number, at first .10 BAC and then lower and lower, as MADD gained influence and legislators had fewer criminal dragons to slay, that condemned people without regard to any real harm.

Prohibition may have failed, but we’ve never really gotten over the moralist’s hatred of evil intoxicating beverages. And this black box made it easy-peasy to nail the culprits.

And then there was the question of why the digital readout number was a real number in any event. Courts blindly relied on the integrity of the magic box, because it seemed very sciency and lawyers love science, even if we know nothing about it. It removes the dilemma of having to think too hard about evidence. Thinking too hard gives people headaches. So does booze. Headaches are bad. Stop the headaches.

But there was a chance, a tiny crack, that we could revisit the efficacy of the beloved black box when a petition for a writ of certiorari was submitted to the Supreme Court of the United States in the case of Terry Vangelder out of San Diego.

The case comes from San Diego County, where Terry Vangelder was stopped by a highway patrolman in December 2007 after driving his pickup truck at speeds of more than 125 mph. With Vangelder’s consent, the officer administered two breath tests that registered .095 and .086 percent. At Vangelder’s trial, the defense offered testimony by Michael Hlastala, a University of Washington professor of medicine and physiology. He said breath-testing machines are unreliable because they measure the content of exhaled air, which can be affected by the rate of breathing and other variables, rather than air that is deep in the lungs and closer to the bloodstream.

Vangelder’s lawyer, Charles Sevilla, argued that the California ruling was “unduly trusting in the infallibility of government testing of these machines.” Unduly, as in the box was handed down to Moses on Mt. Sinai.

As Shaun Martin explains at the California Appellate Report, the magic box is “roughly” reliable.

One reason for the “roughness” is what’s called the “partition ratio”. Simply put, with some people, more booze gets through the aveolar sacs to the lungs, than with other people. This ratio varies from person to person. Women are generally different than men. Lung capacity (and condition) also plays a role. There is, in short, a ton of variability. None of which matters to the Legislature. The Legislature has by definition set the partition ratio at 2100 to 1. We’re going to declare — despite the fact that we know it’s not true — that the amount of alcohol in 2100 parts of breath by volume is equal to the amount of alcohol in 1 milliliter of blood. When you do that, by definition, you know you’re convicting “innocent” people — people who do not, in fact, have a blood-alcohol concentration of .08. Indeed, we’ve done studies, and we know almost exactly how many innocent people we’ll throw into jail as a result.

Martin poses the question of Blackstone’s ratio, that it’s better that 10 guilty men go free than one innocent man be convicted. So we know we’re convicting innocents for drunk driving because the variability of the breathalyzer makes it impossible to do otherwise.

The other way to solve this problem, however, is to do what the Legislature and the California Supreme Court have done here. It’s to say that we don’t care. To define the offense in a way that makes someone guilty even if we know they may not in fact have the characteristics about which we actually care. So we may actually think that .08 alcohol blood content is the dividing line between when you can and cannot be allowed to drive. But we nonetheless won’t define the offense that way. We’ll instead define it as .08 in the person’s breath. That way — by definition — no one’s innocent. Which is what the California Supreme Court says here. Which is in turn why the expert’s testimony is inadmissible to the per se offense at issue.

This is higher math; when the crime can’t be proven because of fallible evidence, redefine the crime to make the evidence infallible. So what if a few innocents are convicted because magic black box says so? Isn’t it worth it to stop drunk driving?

Then again, murder is pretty darned bad too, and yet we don’t tend to water down the burden of proof to make sure that everyone accused can be more easily proven guilty.

Worried about not being able to convict murderers? Just define the offense differently. Say that you’re hereafter guilty of “murder” whenever you’ve (1) actually committed a murder, (2) been found with a gun in your hand within 50 feet of a dead person who’s been shot, and/or (3) have confessed to a murder. Boom. No “innocent” people have been wrongly convicted. By definition.

All of this may strike you as questions worthy of some consideration, particularly given the ubiquity of drunk driving prosecutions, and how many Americans get their first dose of criminal justice after a blow into the magic box. Maybe, just maybe, there could finally be an answer to whether the defense could challenge the magic?

On June 23, 2014, the Supreme Court order list issued.

CERTIORARI DENIED… 13-1012 VANGELDER, TERRY V. CALIFORNIA

No peeking behind that curtain. The black box retains its magic.