"No One Was Supposed to Lose This Much Money on Swiss Francs"

Levine@Bloomberg:

One does not normally see sharp right angles in financial charts, but you could pretty much cut yourself on this chart of the volatility of the Swiss franc against the euro:

Source: Bloomberg (as are the rest)

One straightforward takeaway is: Whoa, that volatility is super high! But perhaps a more useful takeaway is: Whoa, it was super low for a really long time! This is of course because the Swiss National Bank capped the franc's value against the euro: The SNB wanted a price of no less than CHF 1.20 per euro, and the euro itself wanted a price of no higher than CHF 1.20 for reasons of its own, so the result was pretty much a peg at slightly above 1.20. In the 12 months ending on Wednesday, the euro traded in a range of 1.20095 to 1.23640 francs:

That chart looks more jagged than it is, because you're standing too close to it. Here, I've zoomed out by two days:

Those two days -- yesterday and today -- really put the previous year in perspective.

Goldman Sachs Chief Financial Officer Harvey Schwartz said on this morning's earnings call that this was something like a 20-standard-deviation event, and while the exact number of standard deviations is of course a subjective matter, that's the right ballpark. Over the 12 months ended on Wednesday, the annual volatility -- that is, the annualized standard deviation of daily returns -- of the euro/franc relationship was a bit over 1.7 percent; over the last three months of that period the volatility was less than 1 percent.  That converts to a daily standard deviation of something like 0.1 percent.  On Thursday, the euro ended down almost 19 percent, or call it 180 standard deviations, depending on what period you use.

An 180-standard-deviation daily move should happen once every ... hmmm let's see, Wikipedia gives up after seven standard deviations, but a 7-standard-deviation move should happen about once every 390 billion days, or about once in a billion years. So this should be much less frequent. Good news I guess, Switzerland won't be un-pegging its currency for at least another billion years, go ahead and set your Swatch by it....MORE

As a side note, Goldman Sachs may not be very good at figurin' standard deviations.
During the Quant Quake of August 2007 Mr. Schwartz's predecessor, David Viniar, CFO, said something similar:

“We were seeing things that were 25-standard deviation moves, several days in a row”  

Several folks, when they finally quit laughing, pointed out how blatently Mr. V was spinning.
Most however underestimated how infrequent 25SD events are, the most common guess being once in 100,000 years. Tee hee.
In a snappy little eight page paper "How Unlucky is 25 Sigma" we see that at 7 Sigma the odds are:

...The reader will note that as k gets bigger the probabilities of a k-sigma event fall
extremely rapidly:
• a 3-sigma event is to be expected about every 741 days or about 1 trading day
in every three years;

• a 4-sigma event is to be expected about every 31,560 days or about 1 trading
day in 126 years (!);

• a 5-sigma event is to be expected every 3,483,046 days or about 1 day every
13,932 years(!!)

• a 6-sigma event is to be expected every 1,009,976,678 days or about 1 day
every 4,039,906 years;

• a 7-sigma event is to be expected every 7.76e+11 days – the number of zero
digits is so large that Excel now reports the number of days using scientific
notation, and this number is to be interpreted as 7.76 days with decimal point
pushed back 11 places. This frequency corresponds to 1 day in 3,105,395,365
years....

The authors go on to describe the problems involved in computing numbers on the cosmological scales required for 25 standard deviations. A good read, both for the statistically challenged and for pros like Viniar, a very highly paid PR guy, in addition to his CFO duties.

If that link doesn't work  MIT's Physics arXive has

The best of the rest from the Physics arXiv this week

which includes:

How Unlucky is 25-Sigma?