function calcNa(form) {
	if (!checkForm()) return false;
	var fw = document.fw;
	var na = form.na.value;
	var gluc = form.gluc.value;

	if (gluc > 100) {
		na = parseFloat(na);
		var newNa = ((gluc-100) / 100) + na;
		form.correctNa.value = roundNum(newNa,1);
	}

	return true;
}

function checkForm() {
	var fw = document.fw;
	var na = fw.na.value;
	var gluc = fw.gluc.value;
	if (!checkError(na, "na", "sodium (Na)")) return false;
	if (!checkError(gluc, "gluc", "glucose")) return false;
	return true;
}

function checkError(whatVar, varName, varText) {
	if ((whatVar == "") || (whatVar <= 0) || (isNaN(whatVar))) {
		alert("Please enter the " + varText + ".");
		eval("document.fw." + varName + ".focus();");
		eval("document.fw." + varName + ".select();");
		return false;
	}
	return true;
}

function roundNum(thisNum,dec) {
	thisNum = thisNum * Math.pow(10,dec)
	thisNum = Math.round(thisNum)
	thisNum = thisNum / Math.pow(10,dec)
	return thisNum
}