When the fiasco over Facebook’s bungled public offering finally subsides, one very hard question will remain: What are the shares of this companyactually worth?

Given how experienced stock pickers go about their art, the gyrations over the last few days are virtually beside the point. Here’s why:

The last time you bought stock in a company, you probably had a reasonable argument for why you thought its price would rise: the company makes dependable products that people need, it has competent leaders at its helm, the shares look cheap relative to those of inferior rivals, etc. You also might even know (in theory) how sophisticated participants in the market attempt to arrive at a fair value for those shares.

A quick refresher on that last part, just in case: The price of a share of stock is based on how much money a company can potentially earn in the future. Makes sense: Ultimately, companies are only worth something if they can generate positive cash flows; otherwise, the owners should just fire the staff, sell the buildings, furniture and equipment, and move on.

Once you’ve estimated those cash flows, you must convert them to present dollars by dividing them at some appropriate rate equal to the return you might have earned investing your money in a similarly risky venture. That’s it: Estimate the cash streams and discount them to present dollars.

Doing a traditional “discounted cash flow” (DCF) valuation calculation isn’t rocket science, but doing it right requires a fair bit of work and a ton of educated guessing. (There are less rigorous valuation techniques, like price-to-earnings ratios and the like, but DCF is the king.)

Let’s focus on the guessing part of this game, and what it means—or doesn’t—for a company like Facebook.

A valuation model basically comes in two pieces: the earnings to come in the next five years (which you can approximate with some confidence) and the earnings to come all the years after that (which you estimate by waving what amounts to a wet finger in the air). That second piece is called the “terminal value.” Sum up those two pieces, divide by the number of shares, andVoila: you have the total present value of the stock today.

The first piece is hard enough to get a handle on, depending on what industry a company is in. If the company manufactures sheet steel, estimating earnings for each of the next five years is relatively easy—assuming the global economy doesn’t implode or the world doesn’t discover a stronger, cheaper substitute for steel between now and 2017.

If, however, the company makes, say, designer jeans or smart phones, the estimates get a little fuzzier, given how finicky consumers can be. If the company sells online advertising on a social networking platform, well, who knows what that market will look like in the next five months, let alone in the next five years?

Here’s the really unsettling part: The first piece of the valuation model (comprised of the cash flows over the next five years) might only account for aquarter of the overall valuation. The second piece (the terminal value) accounts for the rest, along with the value of any real estate, marketable securities and cash. In other words: Most of the stock price is tied up in the terminal value.

How hard is it to calculate the correct terminal value? Really hard. I won’t derive the formula, but here it is:

           TV = cash flow in Year 6 / (r – g)

In the formula, “r” equals the long-term discount rate, and “g” equals the company’s long-term growth rate (assumed to smooth and flatten over time).

While the arithmetic is easy, you can see how even small changes in that denominator would wildly swing the terminal value.

Consider: In a May 7 research report, Brian Wieser, a Charted Financial Analyst with Pivotal Research Group, kindly provided a matrix of potential valuations for Facebook based on different assumptions for both the long-term discount rate and the long-term growth rate. Just based on changes in the resulting terminal value, Facebook’s valuation would swing between $23 and $81, and the company’s total market value between $59 billion and $207 billion. That’s a big swing. In Wieser’s model, Facebook’s terminal value accounts for fully two-thirds of its overall worth. He thinks Facebook’s shares are fairly priced at $30.

“The change [in price] can be pretty substantial with a change in discount rate or growth rate,” says Wieser. “My philosophy on this: Establish a benchmark you’re comfortable with—in this case, Google—and assess the metrics on discount rate or growth rate by comparison.” He’s right: That’s about all you can do.

So what does all of this glorified guesswork mean for Facebook shareholders and those watching anxiously from the sidelines?

If you’re placing daily bets on Facebook shares (and I sincerely hope most of you aren’t), then obviously you care a lot if they lurch 15% in either direction. But as to whether the company is intrinsically worth $30 or $40 or anything in between, much of what’s in that number, by definition, is noise at the moment.

Social networking is no fad, and Facebook is a giant. It’s worth…something. As to how much, even talented analysts can’t know with precision. Eventually (though probably not for awhile), the company’s cash flows will coalesce around some better-defined trajectory, the valuation models will firm up and comfort levels will rise.

Until then, and if you must, try to enjoy the ride.