It's part of the game rules (see beergame.org). You have to pay extra for keeping your downstream customer happy with more customer relations while you have a backlog to fill their order.

On week 10, incoming 1 week delay had zero being delivered on week 11. Week 11 had an order of 10 requested, inventory of only 5 (on week 10) and zero incoming on week 11. Backlog (inventory) is -5 on week 11 since we could not send out 10 and only sent out 5 (what we had in inventory+incoming) on week 11 (see shipped column).

@@thinkniko Yes I see, but I still don’t know why we don’t put 0 in inventory in 11th week and then in 12th it would be -5, like we did in all the other lines

@@kasiastanczuk6366 Because the order for 10 was not fulfulled in week 11, only 5 of the 10 was shipped so there is a backlog already of -5 on week 11.

@@thinkniko mm okay, thanks for the reply

It handles if the inventory would go negative and if the incoming inventory would satisfy (even partially) the order (and backorders) to ship if the inventory is zero or would be negative. The spreadsheet is viewable and you can look at the formula. After doing a few play throughs testing the sheet with various inputs to see if I can hit all the possible conditions to handle it in the formulas. Ordered more than inventory + incoming = ship inventory and incoming, but make negative inventory for what didn't ship. Backorder (neg inventory) but incoming would satisfy order and backorders = ship order+backorder amounts and inventory should be zero or positive. etc. etc.

@@thinkniko Thanks Niko. ☺️