asterisk users - Aug 2005 - How to determine elapsed time of a call in progress?

Hi all,

I need to be able to determining the elapsed time of a call.
I tried commands like 'show channel' or 'zap show channel', 
this
outputs a list of parameters including 'elapsed time' but for some
reason this is always '0h0m0s'.
Is this normal or am I looking at the wrong place or using the wrong command?

My configuration:
Asterisk 1.0.7 + Bristuffed
The channel which I tried (and need the information for) is the
channel of an agent who is handling a call via the Queue where agent
is member of. This channel is running via the Zaphfc driver via HFC
PCI in NT mode.

Can you give me a hint to my problem?

Thank you!
Michel Koenen