Economist concept of marginal cost vs accountant concept of marginal cost

The concept of marginal cost is not same when an accountant and an economist calculate marginal cost.  An economist define marginal cost is the cost of producing an aditional unit of product. In this case the fixed cost is considered. On the other hand when an accountant calculates marginal cost he never consider fixed cost. An accountant considers marginal cost is constant in per unit of output when aditional number of production is produced. This is not applicable in front of an economist.  In a mote analysis it is found that in increasing of the number of output the cost of the product of per unit of output is decreased. If we plot a graph the cost per unit of output vs production unit, we will find a graph production cost of per unit of output is decreases gradually. With an equation marginal cost can be calculated by substracting fixed cost from total cost.