# Pastebin dwJ2NWam
method Str {
        # cut off exponential denorm logic below a modest value
        my Bool $modest = ( 1/$_ < $!value.abs < $_ ) given $round-cut;

        with self.error {
            my ($value, $error, $scale);

            #| Setting Controlled
            #| >> $round-val controls rounding explicitly (e.g. 0.01)
            with $round-val {
                $scale = $_;
                $value = $.value-rounded;
                $error = $!error.absolute.&round($_);
            }

            #| Error Controlled
            #| >> significant digits of error value control rounding
            $scale //= .scale;

            if $modest {
                $value //= $!value.Rat.round($scale);
                $error //= .absolute.Rat;
            } else {
                $value //= $!value.FatRatStr.round($scale);
                $error //= .denorm;     #right shift error value to align digits
            }

            return "{ $value }{ $.units } ±{ $error }"
        } else {
            # no Error? Setting Controlled!
            return "{ $.value-rounded }{ $.units }"
        }
    }