sub _format_nanosecs {
    my $self = shift;
    my $precision = @_ ? shift : 9;

    my $divide_by = 10**( 9 - $precision );

    my $t = sprintf(
        '%0' . $precision . 'u',
        round( $self->{rd_nanosecs} / $divide_by )
    );
    return ( length($t) > $precision ) ? "9" x $precision : $t;
}