function IsNumeric(strString) {
  //  check for valid numeric strings

  var strValidChars = "0123456789.-";
  var strChar;
  var blnResult = true;

  if (strString.length == 0) return false;

  //  test strString consists of valid characters listed above
  for (i = 0; i < strString.length && blnResult == true; i++) {
    strChar = strString.charAt(i);
    if (strValidChars.indexOf(strChar) == -1) {
      blnResult = false;
    }
  }
  return blnResult;
}