if( ${$sens}{$i}->{"datediff"} ){
	    $dbColName=${$sens}{$i}->{"dbcolName"};
	    $unitFactor=${$sens}{$i}->{"unitfactor"}->{"$dbColName"};

            $midnightDate=${$sens}{$i}->{"datediff"};  # date of day for which to calculate sum
	    $midnightTime="00:00:00";                  # starting from midnight
	    $dayEndTime="23:59:59";		       # Day end time
	    #
	    # Since the database stores dates in GMT we have to calculate what GMT time 
	    # corresponds to the local time "midnight" 
      	    ($midnightDateGMT, $midnightTimeGMT)=timeConvert($midnightDate, $midnightTime, "GMT");
	    # Now calculate what GMT time corresponds to local time "end of day"
      	    ($midnightDate, $dayEndTime)=timeConvert($midnightDate, $dayEndTime, "GMT");
    
	    # Now select data that is between midnight(GMT) and end of day(GMT)
      	    $sql="SELECT SUM($dbColName) AS \"SUM\" FROM $table WHERE stationid = $stationId AND".
	         " datetime>=\"$midnightDateGMT $midnightTimeGMT\" AND".
	         " LEFT(datetime,10) <=\"$midnightDate $dayEndTime\" AND sensid=$sensorId";
	    @res=$dbh->selectrow_array($sql);
            $tmp=$res[0] * $unitFactor;
            $tmp=int($tmp*100)/100;
    	    ${$sens}{$i}->{"sensorval"}->{"$j"}->[0]->{$dbColName}=$tmp;
	 }