private function combineSumPoints($points1, $points2) {
        $pointsCount = count($points1);
        $currPoint = 0;
        foreach ($points2 as $point2) {
            $pointFound = false;
            //leverage the fact that points are sorted and improve O(n^2)
            while ($currPoint < $pointsCount) {
                $point1 = $points1[$currPoint];
                if ($point1['time'] == $point2['time']) {
                    $points1[$currPoint]['sum'] += $point2['sum'];
                    $currPoint++;
                    $pointFound = true;
                    break;
                }
                $currPoint++;
            }
            //point not found in downsampled array, then just append
            if (!$pointFound) {
                $points1[] = $point2;
            }
        }

        return $points1;
    }