Hello Vonasi

Thank you for your reply, but this has nothing to do with automatic trading, I am not using IG but IB broker.
My idea is that, I know we can close the positions at any price we want, but the open price will be the mean of all the positions we opened for the same security, and I find it a little bit far from the reality.
As I said, if I buy 1 share @$10 then another share @$2 (the price dropped) and after some days the price rose again and is now @$3, for me I can close the second position with gains (3 – 2 = +1$), however the platform will consider the mean price of both my positions ((10 + 2) / 2 = 6) so it will be like I bought 2 shares  @$6 and if I sell one share I will be losing money (3 – 6 = -3).
That’s my point. I have two different shares at different prices, I don’t understand why the platform deals only with the mean price.