Average wait for a visa. Trade figures. Tallies of Chinese investment in the United States. These have been Locke's obsessions during his tenure as the US ambassador to China.
It has been a tumultuous time in one of America's most complex and important relationships, and Locke has lived moments of enormous drama - including high-stakes negotiations over a blind dissident hiding out in the US embassy and the attempted defection of a Communist Party insider.
But with just weeks left on the job, Locke believes his legacy lies primarily with those numbers.
He points to the waiting period for interviews for Chinese applying for US visas: less than five days on average, down from as high as 100 days a few years ago. He noted that in the past two years, more Chinese investment has poured into the United States than in the previous 11 years combined.
His theory as ambassador, Locke says, is that by focusing on the details - such as the visa process - you can move the needle on much bigger goals, like exposing more Chinese visitors to American-style democracy and values.
"It's not just the numbers, but what those numbers represent," he says.
Some US ambassadors are known for their influence, like Zalmay Khalilzad, who was dubbed "the viceroy" when he was posted in Afghanistan. Some stand out for their pro-democracy activism, like Robert Ford, who showed support for anti-government demonstrators while serving as ambassador to Syria.
Locke, 63, has won fame as a number cruncher.
Just days after landing in Beijing, Locke asked his embassy section heads for their goals, steps to reach them and ways to measure the progress.
"It was a very practical approach to diplomacy," said one embassy official. "He didn't want esoteric answers but exact explanations."
Locke's approach reflected his experience in politics.
As US secretary of commerce from 2009 to 2011, he reduced lag times in issuing patents. Previously, as governor of Washington state, he cut drivers' licence waiting times from 60 minutes to 10.
Not everything lends itself to such measurements, especially in the world of diplomacy. Deciphering China's opaque leadership structure is often elusive work, and making progress on human rights requires quiet, sustained effort. "But I wanted to make sure we at least outline our goals in those areas," Locke says.
Some US analysts question whether he played a large enough role in shaping China policy.
"He walks away having accomplished something on visas, but in terms of having a policy impact, nothing," said Doug Paal, vice-president of studies at Carnegie Endowment for International Peace in Washington. "He hasn't stood out in a positive or negative way."
But others say that under the Obama administration, the White House and the National Security Council have more aggressively controlled policy on China, leaving less of a role for the American ambassador in Beijing.
Locke says he was one of a group of players involved in big crises, including the negotiations over the fate of blind dissident lawyer Chen Guangcheng, who fled to the US embassy from house arrest in spring 2012. The ambassador's role, Locke says, is to explore and lay out all options for those involved, along with their potential consequences.
Susan Shirk, a former diplomat who is chairwoman of the 21st Century China Programme at University of California at San Diego, says diplomats could spend all their time "doing a little bit of this, a little bit of that, and not end up with much".
"The two things he focused on - investment and visas - they're not insignificant," she says
When Locke arrived in August 2011 and promptly declared visas his top priority, many at the embassy expressed scepticism. Making the process easier would only increase demand. And no additional funding or workers were in sight for several months.
But within two months - by re-engineering the process, including lengthening the working day by organising staff into staggered shifts - embassy employees dramatically decreased the waiting times for visa interviews.
The improvement was crucial in boosting trade, Locke says. "If you're a Chinese businessman, you can't just wait 100 days to get your visa, that's lost business," he says.
In the past two years, the number of visa applications has risen 75 per cent. That's significant for the US, Locke says, because the average Chinese citizen spends US$6,000 during each visit to the United States.
He has similarly sought to overcome other obstacles to Chinese investment. Locke secured money from business groups for a slick video explaining US investment law. Some Chinese companies have been wary of investing in the United States because of well-publicised cases in which their intended purchases have been blocked or met with protests from American politicians. US officials now show the video every chance they get to Chinese business leaders.
Locke also took on the role of matchmaker, getting US business groups and local American economic development agencies to compile books of shovel-ready projects to lug around to Chinese investors. Some analysts say he played a role in the huge increase in Chinese investment, which totalled US$18 billion in the past two years, compared with US$11 billion from 2000 to 2011.
In China, Locke is best known not for his work on trade or visas but for being the first US ambassador in the country who is Chinese American.
Before he even landed in China, photographs of him buying coffee at a Starbucks at the Seattle airport went viral. For Chinese, the image of a US dignitary, who looked ethnically like their own officials, carrying his own luggage and fetching his own coffee made their party leaders seem deeply out of touch.
Locke's personal narrative as the son of an immigrant family who worked his way to a senior government position has also served as a constant promotion of American possibilities.
Even now, Locke is swarmed at events and sometimes asked to pose for hundreds of pictures at a time.
The constant picture-taking wears on him at times, Locke says, "but it makes the people I meet feel good. It's a small price to pay for that kind of personal diplomacy".
With his replacement, Senator Max Baucus, in the confirmation process, Locke plans to leave by March 1. He says he is resigning because he and his wife want to give their eldest daughter a chance to spend her junior and senior years at a US high school.
Locke hasn't decided what he'll do next, but he rules out a run for public office.
As part of his farewell tour, Locke recently made a final pilgrimage to his family's ancestral home among the muddy rice paddies of Taishan in Guangdong. When he arrived in the village, hundreds of people erupted in cheers, and many vied to get one last photo with him.
"I'm just a villager. I don't know anything about US-China relations," distant relative Lok Gufei, 57, said. "But he is our most famous brother. And we are proud of who he is and what he represents."
The Washington PostTopics: Gary Locke