Jobs, resources, and time

A work list is not yet a plan for the shift. At Northstar, a job needs a name, a time, a place, and a clear point when it is ready. We will build that plan on one clock. Zero means the start of the shift. Each time we use is a count of minutes from that point. This keeps a due time and a start time on the same scale, so we can compare them with care. Start with one filler and three jobs. A needs sixty minutes and is ready at zero. B needs forty and is ready at eighty. C needs thirty and is ready at zero. Suppose we choose A, then B, then C. A runs from zero to sixty. B is not ready at sixty, so the line must wait. B runs from eighty to one hundred twenty. C then ends at one hundred fifty. The gap is real. Do not hide it. Now place C in that gap. A still ends at sixty. C can run from sixty to ninety. B is now ready, so it runs from ninety to one hundred thirty. We have used the same run time, but the last finish is twenty minutes sooner. That does not prove this order is best for every goal. It shows why a ready time can matter. Check the due times too before you claim that the new plan is the one to release. A job may need more than one step. Our next case uses a filler and a packer. A needs sixty minutes to fill and thirty to pack. B needs seventy to fill and forty to pack. Both jobs are ready at zero. The filler is closed from one hundred twenty to one hundred fifty. The packer stays open. No task may pause once it starts. We must now obey the route of each job and the clock of each resource. Fill A from zero to sixty and pack it from sixty to ninety. There are sixty open minutes left on the filler before the closure, but B needs seventy. B cannot fit. Wait until one hundred fifty, fill B until two hundred twenty, and pack it until two hundred sixty. A is due at one hundred thirty and B at two hundred sixty. This plan meets both dates. The idle gap may look wasteful, yet it follows the facts we were given. Try B first as a fair test. B fills from zero to seventy and packs from seventy to one hundred ten. A needs sixty minutes, so it also cannot fit before the closure. A fills from one hundred fifty to two hundred ten, then packs to two hundred forty. The last finish is now sooner, but A is late. A shorter day and better service are not the same claim. We need a named goal to choose between those outcomes. Use one line of time for each resource. Put every task on the line it uses. Draw the closure as a block too. A task may end at the exact time the next task starts; those edges do not create an overlap. Then follow each job from its first step to its last. The packer can be free and still unable to pack a job whose filling has not ended. Free time does not remove a route rule. For your lab, keep the raw data next to the plan. Show the start, finish, due time, and wait for each job. Build both orders before you choose one. Then change the one input named in the task and build them again. Do not change other facts to rescue a weak result. A useful plan is one a second person can check, not just one that looks tidy. End with the legal order, the reason for your choice, and the fact that would make you review it. One more check is worth the time. Count each operation once in the job list, and once on each resource it needs. Compare its length with the input row. If the line shows a sixty minute task as fifty, no choice of order can fix that error. Ask a second reader to trace one whole job from release to pack. This small audit turns the picture into a plan that can be used, and gives you a clear place to look when a result seems wrong.

1. Name the jobs

   Original static calculation card for name the jobs, using the Northstar numbers stated in the narration; show labeled units and no decorative charts.

   • A job is not an order twice
   • Name each operation
   • Use minutes from zero
2. Respect readiness

   Original static timeline for respect readiness, using the Northstar numbers stated in the narration; show labeled units and no decorative charts.

   • A ends at60
   • B ready at80
   • Show the20 minute gap
3. Use a shared clock

   Original static calculation card for use a shared clock, using the Northstar numbers stated in the narration; show labeled units and no decorative charts.

   • A-C-B ends130
   • Same130 run minutes
   • Check every due time
4. Link the route

   Original static timeline for link the route, using the Northstar numbers stated in the narration; show labeled units and no decorative charts.

   • Fill before pack
   • Two resource lines
   • No hidden transfers
5. Block the closure

   Original static timeline for block the closure, using the Northstar numbers stated in the narration; show labeled units and no decorative charts.

   • Filler closed120-150
   • B cannot pause
   • Wait for enough open time
6. Choose a legal promise

   Original static calculation card for choose a legal promise, using the Northstar numbers stated in the narration; show labeled units and no decorative charts.

   • A-first ends260
   • B-first makes A late
   • Service and finish differ