This is a rule enforced by EU Omnibus Directive through the "Price Indication Directive" update, that aims to make pricing more transparent for EU customers, particularly when it comes to price reduction announcements. All organizations that do business within the EU must inform their customers about the lowest price within the last 30 days when offering discounts e.g. on Black Friday to reflect market prices before the discount. If you announce a price reduction on a product, you must calculate the discount based on the product's 'prior price' (i.e., the lowest price in the last 30 days or more before the discount was announced). By calculating discounts using prior prices, traders are prevented from artificially inflating prices to give the illusion of a bargain. For instance, if your clothing store offers a Black Friday deal on winter coats, you can't raise the coats' price in the lead-up to Black Friday and then offer a discount on the new, higher price. Instead, you must calculate the Black Friday discount based on the coats' lowest price in the last 30 days or more. Note that the prior price requirement only applies to physical products, not digital ones. Moreover, products that quickly expire or deteriorate (e.g., dairy and fresh fruits) may also be exempt.