public ArabicAbacus(int digitThreshold)
        {
            if (digitThreshold < 1)
            {
                throw new ArgumentOutOfRangeException("digitThreshold", "Digit threshold must be a positive integer");
            }

            this.digitThreshold = digitThreshold;
            rodes = new List<Rode>(this.digitThreshold);
            Rode lastRode = new ArabicRode();

            for (int index = this.digitThreshold; index > 0; index--)
            {
                Rode rode = new ArabicRode(lastRode);
                rodes.Add(rode);
                lastRode = rode;
            }

            rodes.Reverse();
        }
        public ArabicAbacus(int digitThreshold)
        {
            if (digitThreshold < 1)
            {
                throw new ArgumentOutOfRangeException("digitThreshold", "Digit threshold must be a positive integer");
            }

            this.digitThreshold = digitThreshold;
            rodes = new List <Rode>(this.digitThreshold);
            Rode lastRode = new ArabicRode();

            for (int index = this.digitThreshold; index > 0; index--)
            {
                Rode rode = new ArabicRode(lastRode);
                rodes.Add(rode);
                lastRode = rode;
            }

            rodes.Reverse();
        }