Thursday, May 6, 2010

Why Units Are Important

Just to show why it is important to have the right units on numbers, there is a rumor the stock market fell by ~1000 points at one point partly due to a units problem:
According to multiple sources, a trader entered a "b" for billion instead of an "m" for million in a trade possibly involving Procter & Gamble, a component in the Dow...

Sources tell CNBC the firm in question that handled the erroneous trade is Citigroup.
So next time undergraduates complain about they were marked off for having the wrong units, know this error might have cost the market a lot of much money.


  1. ah units! Yes, undergrads and non-nerds alike devalue them, ignorantly believing that the digits are important while ignoring the location of the decimal place. A tragedy indeed.

  2. jmb275 ,

    You know, these days half the theory calculations are done using unit-less quantities.


    That was funny.

  3. "I think the machines just took over. There's not a lot of human interaction"

    We have arrived. As a computer programmer, my work here is done. =:)

  4. Joe -- That's true, and that can be useful as long as you are all on the same page with what unit-less quantities you are using. When you perform calculations with unit-less quantities, that simply means that you are normalizing the quantities such that certain useful physical constants (like c or G) have a value of 1. But there are many different conventions for such so-called "Natural" units. In the end, normalizing c to 1 is no different than normalizing the length of the king's forearm to 1. It's just a different style of units.

  5. Incidentally, in science, some would argue that just like a value without units is meaningless, a value without some measure of uncertainty is almost as meaningless. However, this would be an experimentalist's viewpoint, and is not as widely held, so your personal mileage may vary.


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