Is "volume" the quantity of BTC exchanged, or the number of trades completed? Suppose the following trades happen

Trade 1:   100 BTC  @ $75
Trade 2:   0.5 BTC  @ $76
Trade 3:   100 BTC  @ $77
Trade 4:   100 BTC  @ $78
Trade 5:   100 BTC  @ $78


Five individual trades occurred for a total of 400.5 BTC.  There was a total of 200 BTC acting as a wall at $78.  Similar to how I monitor the trade wall at mtgoxlive.com, I'd like to determine if the "wall moved" or if the "wall was eaten"/traded.  

I'm trying to gather that information from the MtGox website and not sure if they display the count of individual trades, or the BTC sum.

Here, in the top level drop down menu Volume:75584 BTC however in the drop down graph I see volumes that range in 1,000 to 3,000 total.  In the most current example I see a volume 17,261 of something (either trades, or BTC, I'm not sure)



It seems that volume is measured in two ways, but with the same word:


The quantity of BTC shares (and fractional units) traded
The quantity of trades taken (a whole number)


Since MtGox seems to overload the meaning of "volume" in the two instances, where can I find a more accurate representation / graph of each interpretation of "volume"?
They're both representing the same thing over different time periods. The values on the drop down are always for the past 24 hours, the values on the graph depend on what time range you're viewing.

In your example 75584 is the number of bitcoins traded in the past 24 hours, and 17261 is the number traded between 19:00 and 20:00