function Fmt(x) { 
var v
if(x>=0) { v=''+(x+0.00005) } else { v=''+(x-0.00005) }
return v.substring(0,v.indexOf('.')+3) 
}

 
function compute(form) {
var date1 = form.date1.value
var date2 = form.date2.value

var milliDiff = new Date(date2) - new Date(date1);
var period = (milliDiff/3600000)/24;


   	form.hlife.value =Fmt(Math.log(2)*(period)/ Math.log(form.hcg2.value/form.hcg1.value))
if ( form.hlife.value < 0){
	form.hlife.value= "Half life =" + form.hlife.value+" days.";}

 if ( form.hlife.value >= 0){
	form.hlife.value= "Doubling time =" + form.hlife.value+" days.";}




}