docs: public static NumberFormat makeNumberFormat(int digits) {
      // Prefer predefined number formats where applicable.
      // TODO: cache others, too?
      switch(digits){
      case 0:
        return NF0;
      case 2:
        return NF2;
      case 3:
        return NF3;
      case 4:
        return NF4;
      case 6:
        return NF6;
      case 8:
        return NF8;
      }
      final NumberFormat nf = NumberFormat.getInstance(Locale.US);
      nf.setMaximumFractionDigits(digits);
      nf.setMinimumFractionDigits(digits);
      nf.setGroupingUsed(false);
      return nf;
    }