If you think a stock will go down, you may want to sell it short so that ...

>Huh?
You sell a stock you don't own. You just "borrow" the shares from some third party ... in order to sell.
Then, to provide the buyer with the actual shares, you buy the shares a while later. If the stock does go down, you've bought back at a lower price and made money.

>Sell high, buy low.
Right.
Of course, if you're wrong (as I always am) and the stock starts to go up, you'll be scrambling to buy stock at that increased price to "cover your shorts".

>You could lose a bundle if you don't buy quickly, right?
Right again. So it'd be neat if ...

>If you make up a spreadsheet, right?
Uh ... yes, like this:

Click on the picture to download the spreadsheet

You pick a few stocks, click a button and data is collected from Nasdaq.com.
Alas, I have no idea how to download the data to a spreadsheet, so I download, for each stock, the entire webpage (such as this).
Then the spreadsheet picks and saves the appropriate data for each stock. It ain't elegant, but what the heck ...

>The charts show ... what?
The monthly short interest over the past year (so you can see if'n it's going up or down) and, since you'd presumably like to know if 10 million shares is big or small,
the charts also show the ratio:   (short interest) / (average daily share volume).

>So what do you do with that information?
Who? Me? I don't sell short.

However, if'n you're a momentum player and you see everybody is selling a stock short then you may think a lot of people expect the stock to go down so, if you own the stock, then ... >You sell. And if the short interest is way down maybe they're covering their shorts and will buy at any price so ... So the stock may go up. Of course, if you're a contrarian, then ... >But wouldn't you want the short interest and the stock prices ... as a chart? Uh ... good idea. I've added that to the spreadsheet and you get pretty pictures ... like this >And what about the short shares as a percentage of the float, huh? Yeah, that's there too ... so long as the info can be downloaded from here. >Do you believe all this stuff? Who? Me? I don't sell short.