var calc_okno=0;

function show_calc(calc_link,sirka,vyska){
  if(calc_okno){
    calc_okno.close();
  }
  calc_x=((screen.width-sirka)/1.8);
  calc_y=((screen.height-vyska)/1.8);

  calc_okno = window.open(calc_link,"calc_okno","width="+sirka+",height="+vyska+",left="+
  calc_x+",top="+calc_y+",toolbar=0,location=0,directories=0,status=0,menubar=0,scrollbars=0,resizable=0,dependant=1");
}