function isNumberKey(evt)
      {
         var charCode = (evt.which) ? evt.which : event.keyCode
          if (charCode !=45  && (charCode < 45 || charCode > 57) && charcode !=8)
            return false;

         return true;
      }
function mmg()
{
var w = document.form1.w.value;
var t = document.form1.t.value;
var p = document.form1.p.value;
var v = document.form1.v.value;
if((w=="" && t=="" && p=="" && v=="")||(w=="" || t=="" || p=="" || v==""))
{
alert("please enter values for all fields")
}
else
{
var r = 0.0821;
var m = (w*r*t);
var pp=(p*v);
var mm=(m/pp);
document.form1.mm.value=mm;
}
}