// JavaScript Document
function checkForm(form) {

if (form.temp.value < 20 || form.temp.value > 40) {alert("Please enter a temperature between 20 and 40")
return false;}

if ((form.density.value.length>0) && (form.strength.value.length>0)) {alert("Please enter density OR strenth, not both")
return false;}

else return true;
}