Netting and time

A supply plan starts with a simple question. What must be ready, where, and when? It does not start with a new order. First, we need to know what the demand means. Then we need to know which stock can serve it. Northstar makes reusable bottles. Its next week total is fifty one bottles. Twenty of those are firm orders. The other thirty one are still forecast demand. We do not add twenty to fifty one. The twenty are already in that total.

Now add a fact from last week. Six bottles are still owed to customers. Those six are not in the new total. They are a backlog. So the need we must cover is fifty seven. That small word, separate, does real work here. If the fifty one already held the old six, adding them again would be wrong. Good plans show the rule beside the number. They do not leave it in one person's head.

Northstar has eighteen usable bottles on hand. Ten more will be ready before the need. Eighteen plus ten gives twenty eight units of supply. Fifty seven less twenty eight leaves twenty nine. That is the net need. It is a request for more supply. It is not proof that a source can fill it. Keep the need and the firm supply in two fields. This makes the gap clear and keeps hope out of the promise.

What counts as usable? A bottle held for a quality check may be in the building but not ready to ship. A bottle in the wrong place may miss the truck. An open order may be real but late. We need both a status and a date. When an order moves from planned to firm, change its status. Do not add a second copy of the same ten bottles. The plan should follow the goods, not count each new message as more goods.

Now change just one fact. All fifty seven bottles are due on Tuesday, but the ten unit receipt is ready on Friday. At the Tuesday event, Northstar has only eighteen. The gap is thirty nine. At the end of the week, the total gap may still look like twenty nine. Both views can be true. One tells us the final balance. The other tells us who waits. This is why we split a week into days when a close date matters.

There are two sound ways to carry a shortage. In a signed view, the balance can go below zero. That is a signal, not real negative stock. In a physical view, stock stops at zero and the unmet need becomes backlog. Use one method at a time. If you carry a negative balance and also subtract that same backlog next day, you count the gap twice.

Try a small check. Start Monday with eight bottles and demand for twelve. Ship eight. End with zero stock and four backlog. On Tuesday, ten bottles arrive before six new units are due. Use four for the old need and six for the new need. Both stock and backlog end at zero. The signed view starts Tuesday at minus four, adds ten, and takes away six. It also ends at zero. The two views agree.

Your lab builds both views for five days. Do not just copy a formula down a column. Trace which due date each shipment serves. Then move a receipt to a later day. Ask whether final backlog changes, whether on time service changes, and whether both measures tell the same story. A plan can end at the same balance yet serve fewer units on time.

Before you hand over the result, read each total as a sentence. Say what the units are, whose need is included, and when the goods can be used. Check that each order appears once. Keep old due dates when goods are late. These habits make a short table a useful shared record. They also make errors easier to find before a buyer spends money or a customer gets a promise that the chain cannot meet.

Here is one final test to say aloud. If three opening bottles fail a check, how much does the net need rise? It rises by three, from twenty nine to thirty two. The demand did not change. Eligible supply changed.

1. One population

   Two blocks inside one fifty-one-unit demand bar

   • 20 confirmed
   • 31 residual
   • No duplicate
2. Separate old need

   Backlog joins the new-demand bar

   • 51 new
   • 6 overdue
   • 57 total
3. Eligible supply

   Stock and timely receipt reduce a need bar

   • 18 stock
   • 10 receipt
   • 29 net
4. Date matters

   Tuesday need appears before Friday receipt

   • Tuesday cutoff
   • Friday arrival
   • 39 event gap
5. Two ledgers

   Signed and physical balance cards reconcile

   • Negative signal
   • Stock stays zero
   • Backlog separate
6. Audit the handoff

   Five-day ledger with a late-receipt marker

   • Trace each ID
   • Keep due date
   • Explain service