function format_number(expr, decplaces) {

var str = "" + Math.round(eval(expr) * Math.pow(10,decplaces));
while (str.length <= decplaces) {
str = "0" + str;
}

var decpoint = str.length - decplaces;

if(decplaces==0){
return str.substring(0,decpoint);
}
else{
return str.substring(0,decpoint) + "." + str.substring(decpoint, str.length);
}

}