For example, if you buy a fund, the principal 10000 yuan, and the net value is 1.0000 yuan. You can buy 10000 copies without handling fee. At this time, the net cost is 1 yuan, because there is only one sum, and the handling fee is not included. When the net value rose to 1.5 yuan, it bought 1 ten thousand yuan again, with a share of 6666.67. The total share is 16666.67 copies, and the total cost is 20,000 yuan. At this time, the net cost is 20000/16666.67 =1.2 yuan.
Continue to buy in the rise, it will be too high net cost; On the contrary, continuing to buy when falling will reduce the net cost.