Once sale price is calculated do not change it when unit price changes later

Hi Everyone,

I need help to know in the example I send:

a) I have a sell of product "1" in 01-01-2020 , cell "P9" of the ammount of 2,00 €
b) If I change the price of the product "1", for example in 01-10-2020 for 4,00 €, The formula change every sells of product "1". I would like to keep the sell of 01-01-2020 ("P9" = 2,00 €) but the formula will change me every sells of product "1".
Is that possible ?? how can I have the first cell with 2,00 € (old price) and the last sell with 4,00 € (new price).

Thanks

Yes I create a table with dates and prices. The problem is for 2 sells of the same product (in different dates) to keep 1 with the old price and another with the new price.