dhobo, I changed quantity of product to decimal, because I am selling boards, where one size is fixed and customer can enter second size in quantity field (for example 1,25 m). But if customer want two pieces of one board with another sizes, I need to know sizes of both. But presta calculate it, and I see it only as one piece.
Perhaps this could be resolve even with attribute, but I don't found a solution to add attribute, in which the customer entered value.