It took 12 hours and 2,750 shots for Dr. Tom Amberry, a 71-year-old retired California podiatrist, to set the world record for free throws consecutively shot and made.

Over and over, 10 bored witnesses watched his six-second routine — parallel feet, three bounces of the ball, bent knees, tight elbows — in the Rossmoor Athletic Club in Seal Beach, California, on Nov. 15, 1993.

Amberry stopped at the 12-hour mark, but only because the gym janitors made him.

“I could have made a bunch more,” he told The Orange County Register in 1995. “I was ‘in the zone,’ as the kids say.”

In the quarter century that followed, Amberry wowed David Letterman and Tom Brokaw, wrote a free throw guide book, “Free Throw: 7 Steps to Success at the Free Throw Line,” and traveled the globe teaching players how to master the least sexy way to win a basketball game.

Nothing irked him more than sloppy form, poor focus and irreverence. “A free throw is a gift,” he would say. “You should take advantage of it.”

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Coaches, filmmakers and journalists sought his analysis well into his nineties, and more than once he offered critiques from his couch, particularly during the NCAA Tournament.

On Saturday night, in the height of March Madness, Amberry died in California at 94.

Amberry spent his boyhood shooting at a hoop on the side of his barn in Grand Forks, North Dakota, the Los Angeles Times reported in 1995. At 6 feet, 7 inches tall, he played basketball and baseball in high school and graduated in 1940.

He was called off to World War II and spent four years in the Navy, fighting in the D-Day invasion at Normandy and against the Japanese in the Pacific theater. He played on a Navy basketball team.

He returned to California, where he joined the team at City College in Long Beach, California. The Minneapolis Lakers offered him a two-year, no-cut contract. But Amberry turned it down for podiatry school.

For the next 40 years, he didn’t touch a basketball. He and his wife, Elon, raised four sons and in 1991, he retired.

That’s when Amberry got bored. He would wake up, water the yard, stare into space.

“At the end of the day, I felt I didn’t accomplish anything,” he told the LA Times. “I mean, how many times can you vacuum the carpet and get satisfaction from it?”

At the suggestion of a friend, he grabbed a basketball. Amberry heard there were Senior Olympics free throw contests and was determined to qualify.

So he practiced, and studied, and practiced more. Slowly, the retiree improved. He would spend the rest of his life preaching the importance of routine.

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Every morning except Sunday, he began his day at the Rossmoor Athletic Club. He wouldn’t leave until he’d launched 500 shots. “If you’re going to do something, why not be the best?” he once said.

According to his own meticulous records, he consecutively netted all 500 of those shots on 473 occasions.

A 1994 Sports Illustrated profile explained his process of incorporating into his routine pointers from experts as he traveled the country competing.

After he set the record, Amberry made the rounds of the 1990s TV show circuit: Letterman, NBC Nightly News with Tom Brokaw, Jay Leno, ESPN, Ripley’s Believe it or Not.

He was preceded in death by his wife, Elon, and one son, Tim. He is survived by his sons Bill, Tom and Robert; 12 grandchildren and 11 great-grandchildren.

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One sports writer once asked if he was a savant. True to his own gospel, Amberry fired back: “If I am, why do I have to practice so much?”