src/Timer.php
private function calibrate()
    {
        $imax = 20;
        $this->tic();
        $this->tac();
        for ($i=0; $i < $imax; $i++) {
            $this->tic();
            $this->tac(self::RESET_LAP);
            $calib[] = $this->elapsed;
        }
        $this->calib = ArrayUtils::mean($calib);
        $this->stDev = ArrayUtils::stDeviation($calib);
    }
private function calibrate()
    {
        $imax = 20;
        $this->tic();
        $this->tac();
        for ($i=0; $i < $imax; $i++) {
            $this->tic();
            $this->tac(self::RESET_LAP);
            $calib[] = $this->elapsed;
        }
        $this->calib = ArrayUtils::mean($calib);
        $this->stDev = ArrayUtils::stDeviation($calib);
    }
Calculates $this->calib, the average time between immediate calls
to tic() and toc().
Initialises the standard deviation of $this->calib.
@return void