Crystal Reports calculate sum

Message

     I need to calculate sum in datetime group but not all records, only those records that one of the fields are = "55". I created formula:

DateTimeVar prevTime;
NumberVar Result;

If ({ado.RecordType}) = "55" then
  Result:= Result + 1;
If ({ado.localT}) = prevTime then
 Result:=0
else 
 Result:= Result;
prevTime = {ado.localT};
Result;

but its not calculate in time group. What I am doing wrong?

Thanks