function calcRatio(obj) {

   
	if (!obj.gender[0].checked && !obj.gender[1].checked) {
      alert("Click either male or female");
      return; }

   if (!IsNum(obj.hip.value)) {
      alert("Hip invalid");
      return; }
      
   if (!IsNum(obj.waist.value)) {
      alert("Waist invalid");
      return; }
       

   var hip     = eval(obj.hip.value);
   var waist     = eval(obj.waist.value);    
   var ratio = waist/hip;
   
   obj.ratio.value = Math.round(ratio*100)/100
   
   // assess risk.
   var age = obj.age.value;
   
   var risk = "low";
   var modRisk
   var highRisk 
   var veryHighRisk;
   var extra = 0;
   
   // men
   if (obj.gender[0].checked) {
   	modRisk= 		0.83 + (age-20) * (0.91-0.83)/(65-20) 
  	highRisk = 		0.89 + (age-20) * (0.98-0.89)/(65-20);
   	veryHighRisk = 	0.94 + (age-20) * (1.03-0.94)/(65-20);
   	
   	extra = Math.max( 0, (waist - 35)*0.01);
   	
   	// I'm adding this because risk goes up with actual weight 
   	// measurement.  It's a fudge.
   	// I'm ramping up a little more than 1 risk factor.
   }
   else {
   // women
  	modRisk= 		0.71 + (age-20) * (0.76-0.71)/(65-20) 
   	highRisk = 		0.77 + (age-20) * (0.83-0.77)/(65-20);
   	veryHighRisk = 	0.82 + (age-20) * (0.90-0.82)/(65-20);
   	
   	extra = Math.max( 0, (waist - 30)*0.01);
   	
   	// I'm adding this because risk goes up with actual weight 
   	// measurement.  It's a fudge.
   	// I'm adding this because risk goes up with actual weight 
   	// measurement.  It's a fudge.
 	}
   
   if( modRisk < (ratio+extra) ){ risk = 'moderate'}
   if( highRisk < (ratio+extra) ){ risk = 'high'}
   if( veryHighRisk < (ratio+extra) ){ risk = 'very high'}
   
   obj.risk.value= risk;
   
}

// isNum function--------------------------------------

function IsNum(str) {
      for (var i = 0; i < str.length; i++) {
         var chr = str.substring(i, i+1);
         if ((chr < "0" || "9" < chr) && chr != ".")
            return false; 
      }
      if (eval(str)==0)
         return false;
      return true;
   }