function calculateTargetRate(btn){
	var elAge = YAHOO.util.Dom.get("THAge");
	var o = YAHOO.util.Dom.get("targetHeartRate");
	if(!btn || (btn && !btn.id)){
		if(isNaN(parseInt(elAge.value))){
			resetValue(o);
			return;
		};
	};
	if(isNaN(parseInt(elAge.value)) || elAge.value<=0){
		resetValue(o);
		return warnInvalid(elAge,"Please enter a positive number for the activity duration.");
	};
	if(elAge.value>0){
		var rate = parseFloat(220 - elAge.value);
		var low = parseFloat(.65*rate) + parseFloat(elAge.value);
		var high = parseFloat(.8*rate) + parseFloat(elAge.value);
		o.innerHTML = Math.round(low) + " - " + Math.round(high);
	}else{
		resetValue(o);
	};
};
YAHOO.util.Event.addListener(YAHOO.util.Dom.get("THAge"),"keyup",calculateTargetRate);