code: public String dump(Unit unit) {
      StringBuilder buf = new StringBuilder();
      buf.append(unit).append(":\n");
      Map<Unit, UnitFactor> map = factors.get(unit);
      for (Unit base : map.keySet()) {
        UnitFactor factor = map.get(base);
        buf.append("  ").append(factor).append("  ");
        buf.append(factor.rational().compute(RoundingMode.HALF_EVEN).toPlainString()).append('\n');
      }
      return buf.toString();
    }
docs: Debugging conversion factors.