NEW YORK — Movies often take years to travel from idea to completion. Careers are risked. Millions are invested. Armies of professionals are mobilized.

Thanks to immediate box office reporting from theaters, within mere hours of release, it's possible to answer the burning question: Is it a bomb or a blockbuster?

"The opening weekend is torture," says Peter Bart, editor-in-chief of Variety and a former studio producer. "So much is in your hands — maybe 10 years of work. All you can do is watch. It is beyond stress-inducing."

Bart recalls packing into cars with fellow Paramount execs in 1972 to eagerly scope out the opening-day lines for "The Godfather" (one of the first movies to open wide — that is, to be released across the country at the same time).

"It was a very personal business in those days," he says.

Today it's a staggeringly strategic affair that juggles advance polling, demographic-minded scheduling and sophisticated historical models.

But can moviegoers be predicted like hordes of cattle? How accurate are the studio-approved weekend box office grosses? And above all, how much of movie magic can be turned into science?

A movie's box office life begins weeks, if not months, before it's seen by moviegoers. Three research companies — Nielsen NRG, OTX and MarketCast — provide the studios with data that forecast how well a movie is catching on with the public.

This has only recently become widely reported, and it's drawing considerable industry criticism this summer. A recent Variety article declared: "The studios have become keenly aware of cracks in their crystal ball."

The way NRG and company work is based largely on phone calls to survey the public on what films they've heard of and which ones they most want to see. This also provides a demographic breakdown used by studios to find the right release date and maximize exposure to the film's targeted niche.

The tracking can be prescient, or it can miss badly. This summer, "The Break-Up" ($116 million gross) and "The Devil Wears Prada" (expected to pass $100 million) were both expected to do much worse than they did.

Bart, whose recent book "Boffo! How I Learned to Love the Blockbuster and Fear the Bomb" charted the unpredictability of movie mega-hits, doesn't think advance tracking makes movies any less of an (educated) guessing game.

"It'll just have the opposite effect," Bart says. "I think everyone is going to be more and more frustrated because you can't predict it. That's the delicious irony."

However a movie tracks, no one really knows how a film is going to do when the multiplexes open their doors. As they say in sports, "That's why they play the games."

In a recent episode of HBO's "Entourage," Vincent Chase (Adrian Grenier), normally so unflappable, allows himself to get caught up in the opening performance of his (fictional) blockbuster, "Aquaman."

First the numbers look good. Then a blackout hits and disaster looms. This kind of topsy-turvy weekend where stars, agents and producers keep one eye on the numbers is the norm in Hollywood. As Tom Hanks once said, "When a movie opens, everybody is throwing up in wastebaskets."

Though the public typically hears about how well a film opened on Sunday afternoon, or reads the now ubiquitous box office reports Monday morning, studio execs and Hollywood insiders are receiving numbers by the hour as soon a picture hits theaters. After just a few hours, studios know what they can basically expect for the entire weekend.

This is enabled by two reporting services: Nielsen EDI, which has been around for 25 years under varying ownership, and Rentrak, which was formed in 2001. EDI, which collects from 5,600 North America theaters, has traditionally operated with exhibitors calling in their numbers to its phone operators, though it now also takes in results digitally.

Rentrak helped initiate a faster process of hourly updates, fueled by electronic tracking. According to Ron Giambra, head of Rentrak's theatrical group, Rentrak receives data electronically, ticket by ticket, seconds after the sale in 78 percent of theaters.

Come Sunday, both Nielsen EDI and Rentrak send their numbers to the studios, who in turn supply the weekend estimate. Each studio tabulates the estimate for its own film, factoring in the expected gross from Sunday, based on the movie's performance on Friday and Saturday.

That number soon hits every major media outlet in the country. Which action figure slew the competition? Which comedy laughed all the way the bank? For the answers, many news outlets turn to Paul Dergarabedian, the president of box office tracker Exhibitor Relations — and for many, the face of the box office.

"It used to be an industry inside-information kind of thing," he says. "I've seen it really take on a life of its own. It reminds me of anything that gets into the big dollar amounts, like the lottery or stock prices going up.

"People are just fascinated when it comes to these big numbers."