function Thickness() {
  if (document.forms[0].wood_thickness.value == "1") {
    return (1.00);
  }
  if (document.forms[0].wood_thickness.value == "2") {
    return (1.25);
  }
  if (document.forms[0].wood_thickness.value == "3") {
    return (1.50);
  }
  if (document.forms[0].wood_thickness.value == "4") {
    return (2.00);
  }
  return false
}


function CalcAvailableSpace() {
    if (document.forms[0].wood_thickness.value == "0") {
       alert("Please select a Wood Thickness.");
       return false;
    }
    else  {
      volume = (document.forms[0]['height'].value - Thickness()) * (document.forms[0]['width'].value - Thickness()) * (document.forms[0]['depth'].value - Thickness()) / (1728);  
      
      total = Math.round(volume * 1000) / 1000;
      
      {
      document.forms[0]['space'].value = total
      }
    }
}