function conv( val, _from, _to ) {
	
	var val = prepare_in( val );
	
	if( parseInt( _from[_from.selectedIndex].getAttribute( "exc" ) ) ) {
		val = Math.pow( val, "-1" );
	}
	
	var tmp = _from.value / _to.value * val;
	
	if( parseInt( _to[_to.selectedIndex].getAttribute( "exc" ) ) ) {
		tmp = Math.pow( tmp, "-1" );
	}
	return prepare_out( tmp );
}