you want to be very care about this, is your assembly item Serialized? if it is this is going to cause you costing problems as Kevin Mentioned. but thing I can recommend is to space this out over 3 days. Delete the unbuild. This will DECEASE your inventory, the next day Delete the Build This will INCREASE your inventory. on the Third day do you Build. This allows time for the costing engine to process each step. in order. if you do them all at once the costing engine may or mat not do it they way you want. you NEVER EVER want the inventory to go below 1 on any part of the costing will be wiped out.