In Google Keeps Tweaking Its Search Engine, Amit Singhal, master of Google’s ranking algorithm, and other engineers reveal more than they ever have before in the news media about how their search system works.

Here’s a story of how a new formula gets added and why Singhal ignores complaints at first…

In 2005, Bill Brougher, a Google product manager, complained that typing the phrase “teak patio Palo Alto” didn’t return a local store called the Teak Patio.

So Mr. Singhal fired up one of Google’s prized and closely guarded internal programs, called Debug, which shows how its computers evaluate each query and each Web page. He discovered that did not show up because Google’s formulas were not giving enough importance to links from other sites about Palo Alto.

It was also a clue to a bigger problem. Finding local businesses is important to users, but Google often has to rely on only a handful of sites for clues about which businesses are best. Within two months of Mr. Brougher’s complaint, Mr. Singhal’s group had written a new mathematical formula to handle queries for hometown shops.

But Mr. Singhal often doesn’t rush to fix everything he hears about, because each change can affect the rankings of many sites. “You can’t just react on the first complaint,” he says. “You let things simmer.”

Each search match is assigned a numerical score based on more than 200 variables. But Google considers 10 diverse results better than the 10 highest scoring results…

The sites with the 10 highest scores win the coveted spots on the first search page, unless a final check shows that there is not enough “diversity” in the results. “If you have a lot of different perspectives on one page, often that is more helpful than if the page is dominated by one perspective,” Mr. Cutts says. “If someone types a product, for example, maybe you want a blog review of it, a manufacturer’s page, a place to buy it or a comparison shopping site.”

Google’s secret formula? No secret really — they just constantly grind away at it from all different angles…

“People still think that Google is the gold standard of search,” [John] Battelle says. “Their secret sauce is how these guys are doing it all in aggregate. There are 1,000 little tunings they do.”