function calc(form) {

	if (form.max_flow.value.length==0||form.max_RPM.value.length==0||form.cur_RPM.value.length==0) {
		alert('Please fill out all fields to calculate!'); 
		document.cur_flow.max_flow.focus();
	} else {
		form.flow.value=Math.round(form.max_flow.value/form.max_RPM.value*form.cur_RPM.value)+" l/min.";
	} 
}