public function savePeriod($n = 1)
    {
        if (!$this->shouldBeCaptured() || $n < 1) {
            return false;
        }

        // compute the period in question
        $period = $this->nthPreviousPeriod($n);

        // compute the value for that time period
        $value = $this->computeValue($period);

        // generate the start date for the period
        $d = date('Y-m-d', $period[ 'start' ]);

        // save the value
        $stat = new Statistic([$this->key(), $d]);
        if (!$stat->exists()) {
            $stat = new Statistic();

            return $stat->create([
                'metric' => $this->key(),
                'day' => $d,
                'val' => $value, ]);
        } else {
            return $stat->set('val', $value);
        }
    }