The level of output, at which marginal prime cost is exactly equal to the sum of the average prime and supplementary costs, has a special importance, because it is the point at which the entrepreneur's trading account breaks even.

边际主要成本恰好等于平均主要成本和补充成本之和的产出水平具有特殊的重要性，因为这是企业家交易账户收支平衡的点。