Time, calendars, and units

Packing for a picnic feels simple until several tasks need the same kitchen bench. Chopping takes minutes per item, while clearing the bench takes one fixed block. The clock on the wall measures elapsed time, not the sum of everybody’s effort. A planning table works the same way. Keep each type of time visible, and do not assume that two people make one small bench twice as fast.

A capacity number has no meaning without a unit and a period. Twelve minutes per start means that thirty starts use three hundred sixty machine minutes. A half hour changeover contributes thirty more minutes once for the batch. The resulting load is three hundred ninety minutes. Compare that with four hundred eighty usable minutes for the same machine and shift. Headroom is ninety minutes. Do not compare a weekly total with a daily limit, or divide by a count of workers unless the route really permits parallel work.

Usable time must have a clear boundary. If a shift is described as four hundred eighty usable minutes, breaks have already been removed. Subtracting them again understates the capacity. If the calendar instead gives five hundred forty paid minutes and sixty minutes of breaks, the usable total becomes four hundred eighty. Planned maintenance and prior reservations belong in separate rows so another planner can see what changed. Setup may consume both the machine and a skilled person, while unattended run time may consume only the machine.

A fast way to catch unit errors is to write the units next to every multiplication. Starts multiplied by minutes per start produces minutes. Hours multiplied by sixty produces minutes. A utilization percentage is load divided by usable capacity; it is not a count of good bottles. For the example the planned ratio is eighty one point two five percent. High use does not prove good service, because this machine could still wait for caps or finish after the carrier leaves.

If you bake for a school fair, a tray count is not a promise that every cake will be fit to sell. Some may stick or break. You can allow for that when choosing how many to bake, yet you still need to count the good cakes before packing orders. Your oven may also be free on Tuesday but booked on Monday. Extra time in the wrong slot cannot rescue a promise due before it starts.

Northstar has next week demand of fifty one bottles plus six separate prior backlog bottles. Eighteen usable bottles are on hand and ten more arrive before demand. The net requirement is fifty one plus six minus eighteen minus ten, or twenty nine good bottles. If the forecast already contains an order, do not add that order again. Keep old backlog on its own row. A receipt after the due time cannot serve as opening stock merely because it appears in the same weekly report.

At an assumed yield of ninety seven percent, the planning start quantity is the ceiling of twenty nine divided by point nine seven. That equals thirty starts. Expected good output is twenty nine point one, which is an average calculation and not a batch guarantee. Real good output is an integer. If only twenty eight bottles pass inspection, the plan still has a one bottle gap. Do not convert expected output into a firm shipment without inspection or an explicit risk policy.

Calendars tell us when usable work can occur. A resource with an expired qualification cannot be treated as qualified simply because it has spare hours. Likewise, a crew available after the truck departure cannot support that departure. Build separate rows for machine minutes, qualified crew minutes, inspection release, and dispatch cutoff. In this lesson every run starts and ends within its assigned day. More detailed job sequencing belongs in a subsequent scheduling review, but the date gates must already be visible.

In your lab, use three shifts and three dated stock rows. Check one result by hand before you copy a formula. Then cut time in one shift, move a small batch, and delay a receipt. State what changed and what did not. End with a short release note that keeps planned starts, expected good output, and actual good stock apart. That note is the link from a sound calculation to a promise the next team can trust.

1. Define the case

   Original card shows the two lesson titles, fictional business, and planning goal.

   • Northstar case
   • Explicit scope
   • Check the units
2. Read the inputs

   Original table highlights the first lesson’s supplied quantities with unit and timing labels.

   • Given quantities
   • Usable dates
   • Stated limits
3. Trace the first check

   Original arithmetic flow follows the first lesson’s worked calculation to its checked answer.

   • Calculate load
   • Find the gap
   • State the result
4. Add the second view

   Original paired cards show how the second lesson adds a new constraint or decision policy.

   • New condition
   • Same discipline
   • No hidden assumptions
5. Compare scenarios

   Original three-column table uses the lesson lab baseline, stress case, and response.

   • Baseline
   • Stress case
   • Feasible response
6. Release the decision

   Original decision card links result, uncertainty, owner, and next verification gate.

   • Explain tradeoffs
   • Name the owner
   • Verify before release