function isNumberKey(evt)
      {
         var charCode = (evt.which) ? evt.which : event.keyCode
        if (charCode!=46 && charCode!=8 && (charCode < 48 || charCode > 57))
            return false;

         return true;
      }
function bl()
{
var c = document.form1.c.value;
var n = document.form1.n.value;
var cs = document.form1.cs.value;
var t = document.form1.t.value;
if((c=="" && n=="" && cs=="" && t=="")||(c=="" || n=="" || cs=="" || t==""))
{
alert("please enter value for all fields");
}
else
{
var v = (c*n*cs*t);
var cc = (0.082*v);
document.form1.cc.value =(0.082*v);
}
}