public function elapsed(){
        if(isset($this->timeBegin) && isset($this->timeEnd)){
            return number_format($this->timeEnd - $this->timeBegin, 5);
        }
        else{
            if(! isset($this->timeBegin)){
                echo "It is necesary execute the method 'start' first";
            }
            else{
                echo "It is necesary execute the method 'terminate' before";
            }
        }
    }