function calcFW(form) {
	if (!checkForm()) return false;
	var fw = document.fw;
	var nowNa = form.nowNa.value;
	var idealNa = form.idealNa.value;
	var weight = form.weight.value;
	var wtUnits = form.wtUnits.selectedIndex;

// Convert weight to kg
	if (wtUnits == 1) {weight *= 0.45359}

	var fwVal = 0.6 * weight * ((nowNa / idealNa) - 1);

	form.fw.value = roundNum(fwVal,1);
	return true;
}

function checkForm() {
	var fw = document.fw;
	var nowNa = fw.nowNa.value;
	var idealNa = fw.idealNa.value;
	var weight = fw.weight.value;
	if (!checkError(nowNa, "nowNa", "current sodium (Na)")) return false;
	if (!checkError(idealNa, "idealNa", "target sodium (Na)")) return false;
	if (!checkError(weight, "weight", "patient's weight")) 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
}