Probability of Fed rate hike

After noticing all this buzz like "investors are pricing in an x% probability of an august 8 rate hike...." I had to wonder: how is this probability derived, and is there some futures ticker symbol for the probability? Im pretty sure there is; I saw something like this on CNBC a few weeks ago. If I'm not mistaken, the symbol was something like @FED.P or something. Googled it... got nothing. Any input appreciated.

Oh and a side note... check out today's Journal.. what looks like a little filler article talks about Bernanke's assets and salary; he makes $183,500/year

to do the calculation is not that easy. it took me about an hour to build the calculator in excel and i am pretty experienced with that sort of thing. id post the excel file but its not very user friendly and requires knowlege of how the calculator was built and how the fed funds contract works to use it.

if you want to do the calculation, you will need the the quotes on all fed fund futures contracts for the out months.

this is the base forumula you will use...

current rate * the fraction of the month during which the target is known + (projected rate * X + current rate * (1-X)) * fraction of the month during which the target is unknown = Fed Funds Probability