function numericOnly() {
    // deal with unicode character sets
    var unicode = event.charCode ? event.charCode : event.keyCode;
    // if the key is backspace, tab, or numeric
    if (unicode == 8 || unicode == 9 || (unicode >= 48 && unicode <= 57)) {
        // we allow the key press
        return true;
    }
    else {
        // otherwise we don't
        return false;
    }
}