How do I read the log file?

[system]

Hi all

I’m trying to understand how many calls we receive every day. We have this log (taken from the “203” phone, the phone we use to answer calls)
2shared.com/document/LHTgU6DR/log.html
Is it correct to make a filter on the G column “context” --> only “ext-group” and then a filter on the H column “duration” > 0.

Thanks in advance and sorry for this very newbie question