var maxhr = 0;

function displayHr() {
	hrage1 = document.getElementById("hrage").value;	
	maxhr = 220 - hrage1;
	
	if(document.getElementById("hrage").value == "") {
		document.getElementById("maxhr").innerHTML = "<span class='blue'>Please enter your Age before clicking Calculate</span>";
		document.getElementById("hr80max").innerHTML = "";
		document.getElementById("hr90max").innerHTML = "";
	} else {
		document.getElementById("maxhr").innerHTML = "Your maximum Heart rate is <b>" + maxhr + " BPM</b>";		
		document.getElementById("hr90max").innerHTML = "@ 90% Max <b>" + (maxhr * 0.9).toFixed(0) + " BPM</b>";
		document.getElementById("hr80max").innerHTML = "@ 80% Max <b>" + (maxhr * 0.8).toFixed(0) + " BPM</b>";
	}
}