function osmolCalc(form) {
	var na = Number(form.Na.value);
	var k = Number(form.K.value);
	var bun = Number(form.BUN.value);
	var gluc = Number(form.gluc.value);

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

	if ((k == "") || (isNaN(k)) || (k == null)) {
		form.K.value = "";
		k = 0;
	}

	if (k < 0) {
		alert("WARNING: Please enter a potassium concentration.");
		form.K.focus();
		form.K.select();
		return false
	}

	if (!checkNum(bun,"BUN")) {
		form.BUN.focus();
		form.BUN.select();
		return false
	}

	if (!checkNum(gluc,"glucose")) {
		form.gluc.focus();
		form.gluc.select();
		return false
	}

	var osmol = (2 * (na + k)) + (bun / 2.8) + (gluc / 18);
	osmol = Math.round(osmol);
	form.osmol.value = osmol;

	return true;
}


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