code: protected UnitFactor resolve(Unit from, Unit to) {
      if (from == to) {
        return new UnitFactor(Rational.ONE, to);
      }
  
      List<UnitFactor> path = getPath(from, to);
      if (path.isEmpty()) {
        throw new IllegalStateException("Can't find a path to convert " + from + " units into " + to);
      }
      UnitFactor factor = path.get(0);
      int size = path.size();
      for (int i = 1; i < size; i++) {
        factor = factor.multiply(path.get(i));
      }
      return factor;
    }
docs: Find the best conversion factor path between the FROM and TO
  units, multiply them together and return the resulting factor.