Drinking and driving. Many of us have done it. Some of us have gotten busted for it. A few of us have been in life-altering accidents because of it.

Newspapers publish stories about DUI drivers nearly every day. But what does it take to reach the legal limit, and how does alcohol affect us?

We decided to conduct an experiment. Under the watchful eyes of the California Highway Patrol, two Register newsroom employees became inebriated. Along the way, they took tests, interacted with cops and coworkers and talked about their condition.

One participant was Register columnist and copy desk chief Michelle Choat, in her late 20s, of average height, with a slim build. The other was American Canyon Eagle Editor Michael Waterson, who is taller and larger than Choat, of average height and build, and in his late 50s.

The law enforcement presence included CHP officers Jaret Paulson and Jon White, along with Napa Police Sgt. Tom Pieper.

The drink of choice was syrah, a full-bodied red wine which in this case had an alcohol content of about 14 percent.

Register staffers, some there for the duration, others drifting in and out, witnessed what Paulson called the “wet lab” in the conference room at the Register.

The lab included field sobriety tests the CHP administered, as well as an eight-second blow into a Breathalyzer after the participants consumed each 5-oz. glass of wine. The Register added a brief editing test and asked Waterson and Choat to display their dexterity by playing Operation, using tweezers to remove the bones of the patient in the old board game.

Beforehand, both Choat and Waterson ate normally.

They said they expected to reach .08 percent after only a couple of drinks. In fact, their results varied widely.

Choat passed the legal limit, a blood-alcohol level of .08, after drinking three glasses of wine in about 90 minutes.

To the untrained eye, even after three glasses she performed her field sobriety tests reasonably well. The officer conducting the tests, however, spotted tell-tale signs of impairment after two glasses, when Choat’s blood-alcohol level was about .05.

After three drinks, Waterson’s blood-alcohol level had crept up to only .03. Still, he struggled with some of the tests after two glasses.

The experiment was not designed to display what falling-down drunk looks like. “Anyone can see that person and say, ‘That person should not be driving,’” Paulson said.

The officers said the test shows that drinking alcohol impairs us all, but that precise levels of intoxication vary for many reasons. When police make a DUI stop, they use several tools — the breathalyzer, the field sobriety tests, the person’s answers to questions and their appearance — to determine whether to make a DUI arrest.

Here’s what happened in our test.

Baseline

As soon as officers make contact with an apparently impaired driver, they take in a number of factors in deciding whether to make an arrest, Paulson said.

How was the person driving when pulled over?

Did he or she seem scattered or repeat phrases? Did the person have trouble finding his or her driver’s license, registration and proof of insurance? How well did he or she follow directions and perform on the tests?

All this leads officers to ask themselves a common-sense question, said Paulson: “Long story short, would I feel comfortable with this person driving down the road next to me?”

Choat and Waterson took several tests before they started drinking.

Waterson proved his sobriety when an officer asked him to follow his finger with his eyes — the so-called horizontal nystagmus test. But he faltered while asked to balance on one leg to a count of 10. In the field, his performance on that test alone might have falsely indicated that he was impaired, said Officer White, who conducted most of the tests. “That’s a prime example of why we do so many tests,” he said.

Even sober, performing the tests was unnerving, Choat said afterward.

“I can see failing some of those tests out of pure panic,” she said.

Most people are nervous when they are pulled over, Paulson acknowledged. But he said that puts nearly all of them on the same playing field.

Waterson and Choat both caught all seven grammatical, spelling and punctuation mistakes introduced into a couple paragraphs of text.

One drink

After consuming one five-ounce glass of wine in 25 minutes, the color already had begun to appear in Choat’s cheeks. She grew more expressive, but she spoke clearly and coherently.

Waterson’s poise all but masked his first glass.

Both said they felt relaxed as the warming effects of alcohol took hold.

Choat caught all the mistakes in the second editing test, but also corrected one item that wasn’t a mistake. Waterson missed one of the errors in the text.

They took turns blowing into a Preliminary Alcohol Screening Device, commonly known as a Breathalyzer.

Waterson’s blood-alcohol content was .018 percent. Choat’s was .027 percent.

The difference didn’t surprise Paulson or White.

Many factors play into people’s blood-alcohol content.

Their gender, how much they’ve eaten, their height and weight, their metabolism, the kind of alcohol consumed, when they finished their last drink and what medications they use are among the influencing factors, White said.

One person’s results could vary from one day to the next, said Paulson.

“There’s so many subjectives in the entire process,” White said. “It really comes down to individual cases and individual investigations.”

Two drinks

After two glasses of wine, Waterson said he was feeling mellow. He could tell he’d been drinking but felt like he would be capable of driving, he said.

Choat wasn’t sober, but didn’t feel drunk, she said. She said she was at the point where she still might decide to drive home after a dinner party, but with hesitation.

White had Waterson perform a hand-pat test, instructing him to slap one hand, alternating between palm up and palm down, into the open palm of the other hand while counting “one, two, one two” and speeding up as he went.

Waterson started out smoothly, but after he sped up, he stopped counting. White pointed out that he wasn’t turning his hand completely, instead “chopping” his open palm with the side of his hand.

Waterson was asked to touch his thumb to each fingertip on one hand, counting from one to four, forward and then backward. White told him to perform the test three times. White stopped Waterson after he had kept going, repeating the test nine times.

Choat was asked to balance on one leg while counting “one thousand one, one thousand two.” She performed the test without problems, but admitted it helped that she had heard the officers previously explain the directions to Waterson. Still, the signs of alcohol were evident: bloodshot eyes, flushed cheeks and a slight blur of the edges of her words.

“If I just looked down, and made a quick observation, I can see she’s been drinking,” Paulson said.

Choat’s blood-alcohol level had doubled to .053 percent. Surprisingly, Waterson came in at .011 — lower than his first test. Waterson’s body was absorbing the alcohol faster than he was drinking it, Paulson said.

But Paulson predicted Waterson would reach “maximum absorption” and his blood-alcohol content would begin to climb again.

Three drinks

After one more glass of syrah and about 100 minutes into the test, both Waterson and Choat knew they were too impaired to drive.

“I feel like I should not drive anywhere,” Choat said. “I feel very giddy.”

Redness had crept into both people’s eyes, and the scent of fermented grapes permeated the conference room.

The same happens inside a car, Paulson said, though people accustomed to the space may not notice it.

Choat blew a .085, while Waterson was only at .03.

White asked Choat the questions he would pose on the shoulder of the highway — where she had been, how much she had to drink, what her medication regimen was and how she felt.

She second-guessed her own answers and asked questions about the questions. Although Choat knew she was in a test and her responses reflected confusion on whether to answer as a test-taker or a would-be driver, this behavior is typical of people who have been drinking, Paulson said.

Choat followed the officer’s finger with her eyes. She did the palm slap. She tilted her head back, closed her eyes and estimated 30 seconds.

She walked a line, stepping from heel to toe, pivoted and walked the line again.

Choat and observers thought she performed the tests well.

White agreed there weren’t significant problems, but said there was plenty of evidence she’d been drinking.

She swayed slightly while walking the line, shifting her weight too much.

She missed the tip of her nose the first couple times she tried to find it. She raised her arms to balance while holding one foot up.

Her impairment was most obvious in the test she could not control at all, where her eyes followed his finger as we waved it slowly across her field of vision.

A sober person’s eyes follow smoothly, but the eyes of someone under the influence tremble involuntarily, especially at the peripheries.

“The eyes can’t lie,” White said. “There’s nothing you can do about it.”

Choat thought she did well on the tests, but said they were more difficult than they had been earlier.

“I felt that I was thinking a lot more,” she said. “I was really focussed on everything that he said because I knew that every step counted.”

Choat missed two errors on the editing test and introduced one of her own. Waterson caught four of the seven mistakes.

Overall, Register Editor Bill Kisliuk said the pair did pretty well on the editing tests, but their performance had deteriorated, especially after two glasses.

“I think the change had more to do with the social effects of the alcohol, chattering and not concentrating, than it did with any loss of brain power,” he said.

Although Waterson wasn’t technically over the legal limit, he knew he had crossed another line.

“I would be very reluctant at this point to get behind the wheel.” Waterson said.

One more

It was 2:50 p.m., more than two hours after the test started, when each finished their fourth glass of wine.

Observers guessed Choat was maybe .10, but she blew a .122. Waterson, ever quieter, was still below the legal limit at .06 percent.

Neither had many problems playing Operation throughout the lab.

In only a couple instances did the buzzer sound, indicating the surgery had gone awry.

The officers pointed out that people often can concentrate on a single task when impaired. But when asked to do more than one — perform a physical test and remember exactly how many times to perform it, for example — they falter.

The test was over. The bottle of Napa syrah was empty.

A glass or two remained in the bottle from Santa Barbara County.

Paulson and Pieper made some additional points and showed a brief, but gruesome, video of what can happen in an accident if even one passenger doesn’t wear a seat belt.

Co-workers drove Waterson and Choat to their Napa homes, and the pair promised not to go out for the rest of the day.

The morning after

In the following days, both participants said the lab was a wake-up call, despite their varied results.

Waterson called it a “sobering experience.” He said he will think twice before having a second glass of wine when he must drive.

He was surprised at how poorly he did at the field tests although he was well under the legal limit. “That has to give you pause ... Wow, if I’m that bad at being able to clap my hands and touch my nose, what’s that do to my ability as a driver?” he said.

Choat said she wonders how often she may have approached the line to impairment. “I need to be much more careful in real life,” Choat said.

Paulson noted that the experiment also shows the limits of bystanders’ abilities to judge others. Choat’s performance on the field tests, even when she was .085, didn’t scream that she was impaired.

Paulson said he was not sure he would have been “running over to stop her” if she went to drive.

“Just because someone isn’t tripping or stumbling doesn’t mean someone is OK to drive a car,” he said.

Waterson, although he never reached the limit, still might have been a candidate for a drunk driving arrest, Paulson said.

“Looking at him, I don’t know if I would have felt comfortable with him driving,” he said.

In the real world, each case is a judgment call, the officers said.

A driver blowing a .08 makes an arrest a sure thing — whether you are in your own driveway or miles from home — but officers look at all the factors before making a decision in cases where the line is blurred.

There’s too much at stake, including the safety of the drivers and others, to let impaired drivers go.

“This is a big decision,” Paulson said. “This potentially could change this person’s life ... I think we’re going to err on the side of caution.”