Is falling when marginal cost is below it and rising?

When marginal cost is below average total cost, average total cost tends to fall, as each additional unit produced is less expensive than the average of previous units. Conversely, when marginal cost is above average total cost, average total cost rises, since producing additional units adds more cost than the average. Thus, if marginal cost is falling while it is below average total cost, it could lead to a further decrease in average total cost, while rising marginal cost above average total cost would increase it.