function checkNum(toCheck) 
{
  var isNum = true;
  if ((toCheck == null) || (toCheck == "")) 
  {
    isNum = false;
    return isNum;
  }
  for (i = 0; i < toCheck.length; i++) 
  {
    if ((toCheck.substring(i,i+1) != "0") &&
        (toCheck.substring(i,i+1) != "1") &&
        (toCheck.substring(i,i+1) != "2") &&
        (toCheck.substring(i,i+1) != "3") &&
        (toCheck.substring(i,i+1) != "4") &&
        (toCheck.substring(i,i+1) != "5") &&
        (toCheck.substring(i,i+1) != "6") &&
        (toCheck.substring(i,i+1) != "7") &&
        (toCheck.substring(i,i+1) != "8") &&
        (toCheck.substring(i,i+1) != "9") &&
        (toCheck.substring(i,i+1) != ".")) {
      isNum = false;
    }
  }
  return isNum;
}

function checkFieldNum(field)
{
   if(!checkNum(field.value))
   {
      alert("Wszystkie warto\u015Bci musz\u0105 by\u0107 liczbami. Nale\u017Cy wpisa\u0107 liczb\u0119 w prawid\u0142owym formacie.\n Je\u015Bli jest to liczba u\u0142amkowa wpisz liczb\u0119 ca\u0142kowit\u0105 kropk\u0119 oraz warto\u015B\u0107 u\u0142amka dziesi\u0119tnego.");
   }
}

function checkFormNum(form)
{
   var isNum = true;
   
   for(field = 0; field <= 2; field ++)
   {
      if(!checkNum(form.elements[field].value))
	  {
	     isNum = false;
	  }
   }
   if(!isNum)
   {
      alert("W formularzu brak kompletu danych lub wpisa\u0142e\u015B niew\u0142a\u015Bciwy format liczb!\n Je\u015Bli warto\u015B\u0107 jest liczb\u0105 u\u0142amkow\u0105 wpisz liczb\u0119 ca\u0142kowit\u0105 kropk\u0119 oraz warto\u015B\u0107 u\u0142amka dziesi\u0119tnego.");
   }
   return isNum;
}

function calculate(form) 
{
  if(checkFormNum(form))
  {
     with(form)
	 {
	    koszt.value = cjedn.value * 36000 / (wopal.value * sprawn.value/100) + "z\u0142"
	 }
  }
}