function fenaCalc(form) {
	var PNa = form.PNa.value;
	var UNa = form.UNa.value;
	var PCr = form.PCr.value;
	var UCr = form.UCr.value;

	if (!checkNum(PNa,"plasma sodium")) {
		form.PNa.select();
		form.PNa.focus();
		return false
	}

	if (!checkNum(UNa,"urinary sodium")) {
		form.UNa.focus();
		form.UNa.select();
		return false
	}

	if (!checkNum(PCr,"plasma creatinine")) {
		form.PCr.select();
		form.PCr.focus();
		return false
	}

	if (!checkNum(UCr,"urinary creatinine")) {
		form.UCr.select();
		form.UCr.focus();
		return false
	}

	var FENa = (UNa * PCr) / (PNa * UCr) * 100;
	FENa = rounding(FENa,1);
	form.FENa.value = FENa;

	var rfi =  (UNa * PCr) / UCr;
	rfi = rounding(rfi,1);
	form.rfi.value = rfi;

	return true;
}

function ttkgCalc(form) {
	var pk = form.pk.value;
	var uk = form.uk.value;
	var posm = form.posm.value;
	var uosm = form.uosm.value;

	if (!checkNum(pk,"plasma potassium")) {
		form.pk.select();
		form.pk.focus();
		return false
	}

	if (!checkNum(uk,"urinary potassium")) {
		form.uk.focus();
		form.uk.select();
		return false
	}

	if (!checkNum(posm,"plasma osmolality")) {
		form.posm.select();
		form.posm.focus();
		return false
	}

	if (!checkNum(uosm,"urinary osmolality")) {
		form.uosm.select();
		form.uosm.focus();
		return false;
	}

	if (posm > uosm) {
		alert("Urinary osmolality must be GREATER than plasma osmolality for the TTKG to be valid.");
		return false;
	}

	var ttkg = (uk / pk) / (uosm / posm);
	ttkg = rounding(ttkg,1);
	form.ttkg.value = ttkg;

	return true;
}


function checkNum(val,text) {
        if ((val == null) || (isNaN(val)) || (val == "") || (val < 0)) {
                alert("Please enter a " + text + " concentration.");
                return false
        }
        return true;
}


function rounding(number,decimal) {
        multiplier = Math.pow(10,decimal);
        number = Math.round(number * multiplier) / multiplier;
        return number
}