function compute(){
   var f = self.document.f;
	
	
	age = f.age.value;
	   if (!chkw(age)){
	     alert("Please enter a number for your age.");
	     f.age.focus();
	     return;
	   }
	
	if (f.gender[0].checked)	//male
	{
		if (f.bodyfit[0].checked)
			max_rate = 220 - age;
		else
			max_rate = 205 - age / 2;
	}
	else
	{
		if (f.bodyfit[0].checked)
			max_rate = 226 - age;
		else
			max_rate = 211 - age / 2;
	}
	showdiv("calculatorresults");

   document.getElementById("maxrate").innerHTML = Math.round(max_rate);
   document.getElementById("targetlow").innerHTML = Math.round(max_rate * 0.6);
   document.getElementById("targethigh").innerHTML = Math.round(max_rate * 0.8);
}