How to get sum of time duration of group records in group footer in crystal reports?

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C#

ASP.NET

CrystalReports

I am designing crystal report with a column having time duration.

I have column like Empcode, name, duration, remarks, etc.

I am grouping report according to empcode.

I want to display sum of duration in group footer.

I have two formulae for that...

 @get_seconds :
   local stringvar array completetime;
    local numbervar totalseconds;
    completetime:=split({DailyAttendance.TotalDuration},":");
    totalseconds:= (3600*cdbl(completetime[1])) + (60*cdbl(completetime[2]));

@total_duration :
   replace(cstr(Sum ({@get_seconds})\3600),".00","") 
   + ":" +  replace(cstr((Sum ({@get_seconds}) mod 3600)/60),".00","")

I am displaying @total_duration in group footer, but i am getting sum of all records in report, not sum of records in group only. Can someone tell me how to achieve this??

Thanks..