function validate(field) {
  var valid = "0123456789"
  var ok = "yes";
  var temp;
  for (var i=0; i<field.value.length; i++) {
  temp = "" + field.value.substring(i, i+1);
  if (valid.indexOf(temp) == "-1") ok = "no";
  }
  if (ok == "no") {
  alert("Invalid entry!  Only numbers are accepted!");
  field.focus();
  field.select();
     }
  }