In sales report given in reporting section in sales app, Margin is calculated based on order lines for particular variant ,means unit price - (cost in sales order line)..
Now cost in sales order line is taken based on product onchange (from product variant form).
But in Real time valuation with FIFO.Cost price in product variant is updated once there is an outgoing.so cost price is not updated yet while you are doing sales ,and leading to wrong margin in the Sales report.
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For example :
let say product variant  x have 58.5 as cost price in form view.Now i purchased a new unit with 78.
but still cost in product variant is 58.5(because it will update once i do the sales/delivery.)

Now when i create sales order ,odoo will take 58.5 as cost in order line based on product variant  onchange. While it should be 78.
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Is this a real issue with Real time -FIFO or i am doing something wrong ?
If it's the issue is there any solution .
And also i don't understand logic behind updating cost after delivery order is done .Is there any particular reason ,odoo has done it in such way ?