public function add(Distance $b)
    {
        return Distance::m(bcadd($this->m, $b->m), static::$s);
    }
public function add(Distance $b)
    {
        return Distance::m(bcadd($this->m, $b->m), static::$s);
    }
public function add ( Distance $ b ) { return Distance :: m ( bcadd ( $ this -> m , $ b -> m ) , static :: $ s ) ; }
Adds another distance to this instance and returns a new instance with
the sum.

@param Distance $b Distance to add

@return static Sum of the two distances
Adds another distance to this instance and returns a new instance with the sum .