let et = match e.kind() {
    std::num::IntErrorKind::Empty
        => "input argument is empty",
    std::num::IntErrorKind::InvalidDigit
        => "invalid charater in timestamp (digits only, ',.' allowed but ignored)",
    std::num::IntErrorKind::PosOverflow
        => "input timestamp too large (is it a real timestamp?)",
    std::num::IntErrorKind::NegOverflow
        => "input timestamp too small [negative] (is it a real timestamp?)",
    _ => panic!(),
}

#[derive(Debug)]
pub enum Precision {
    Seconds,
    Millis,
    Micros,
    Nanos,
}

impl fmt::Display for Precision {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        let text = match self {
            Self::Seconds => "seconds",
            Self::Millis => "millis",
            Self::Micros => "micros",
            Self::Nanos => "nanos",
        };
        write!(f, "{}", text)
    }
}

.help_heading("OPTIONS")
            .arg(Arg::new("precision")
                .short('p')
                .long("precision")
                .value_name("PRECISION")
                .about("The seconds/millis/etc precision to display")
                .takes_value(true)
                .possible_values(&["seconds", "millis", "micros", "nanos", "auto"])
                .default_value("auto"))