Crystal Reports Total Seconds formula help

Message

     I think ive noticed something wrong with my Total Seconds formula and I want to run it passed an expert if I could.  Its part of a multiple formula report so I think I am not calculating it right. 

//Starttime Formula
DateTimeVar StartTime;
If {Reports_Events.Type} = 'start' then StartTime := {Reports_Events.Timestamp};
StartTime

//Duration Formula
If {Reports_Events.Type} = 'Stop' Then DateDiff('s',{Reports_Events.Timestamp}, {@startTime})

//Convert to positive.  For some reason some of my numbers were negative when the duration all should be positive.
if {@duration} < 0 then ({@duration} *-1);

//TotalSeconds formula
local NumberVar TotalSecs;
TotalSecs:= {@ConvertToPositive}

My cross tab is pulling the sum of TotalSeconds.  I think that it could only be pulling the negative numbers converted to a positive.  Is there a formula I can use to Add the negative numbers after they have been converted and the duration that are already positive?

Thanks guys!