time in storm

[hjh]

Hi, I need to know exact time delay in storm. For example, I have a 
topology like SpoutA->BoltB>BoltC. First I collect the time when SpoutA 
emit the tuple, and then in BoltB and BoltC, each will collect the time 
when the new tuple arrives and when the tuple is emitted to the next 
tuple. In this way, I can get t-SpoutA-Emit, t-BoltB-NewTuple, 
t-BoltB-Emit, t-BoltC-NewTuple and t-BoltC-Emit. Then the process delay 
and the transmit delay can be calculated. How ever when I use this 
method to get the delays, some delays are negative. For example 
t-BoltC-NewTuple minus t-BoltB-Emit may be negative. I use 
System.currentTimeMillis() to record time. Can anybody help to figure 
out why this happens?

Another question is about the capacity in the Storm UI, if the capacity 
of a bolt is less than 1, say 0.7, does that mean some times the bolt 
has to wait for new tuple?

Thank you very much!!!