Lesson 9 finished the four-layer flow diagram. This lesson puts a number on it and asks whether the flow holds. The one outcome every student must leave with is the margin habit: a calculator output is a starting point for judgment, not a specification. The strong-math students are the ones to watch here. They'll run the numbers cleanly and skip the margin, and they'll do it with total confidence. Your job is to make the solutioning-versus-final-engineering distinction land on every calculator touch, and to protect the deferral so the class doesn't wander into sorter speed. That's Lesson 25.
| Segment | Min | What happens |
|---|---|---|
| Open on the wrong number | 5 | Read the hook. Put it on the board: a number can be arithmetically correct and still wrong for the building. Ask the room to name why a calculated rate misses in the field. Steer them toward slippage without handing it over yet. |
| Theory versus real-world, and the 3W | 8 | Slippage, then margin. Run the Three W's guessing game on theoretical versus real-world rate before you show the card. Land the solutioning rule: plus or minus ten percent, confirm capability, don't set specs. |
| The three outputs, live | 12 | Run Gap Produced, Theoretical Rate, and Pitch in the Product Spec Calc with the Calc Logic Guide's own numbers. Make each student run them once, not just watch you. Stop at these three. Name the deferral out loud. |
| The margin exercise | 12 | Key teaching moment, below. The 25 CPM slippage calculation. This is the center of the lesson. Don't skip it to save time. |
| Design target versus average | 6 | Average isn't a design target. Set the design-rate debate up here so it's loaded for Riverside: full peak or a documented percentage of peak, decided on purpose. |
| The five-question stress test | 9 | Run the script out loud against a flow on the board. No calculation. The point is that a flow that fails these gets redesigned, not re-equipped. Push on wave release and the exception path. |
| Riverside and close | 8 | Set 20 CPM explicitly, split 55/35/10, sanity-check the standard case, then run the stress test on Riverside's flow. Collect the design-rate defense below. |
| Total | 60 | Baseline session. Expand with the stretch options below if you have 90 minutes. |
Give the room a throughput requirement of 25 CPM and a product mix, and run it live in the Product Spec Calc. Have them size the belt speed and gap so Theoretical Rate lands right at 25 CPM, no margin. Then ask the question that builds the whole habit: what's your actual rate if the belt slips eight percent?
Walk it out on the board. A belt that slips eight percent moves the package at roughly ninety-two percent of commanded speed, so a line sized to exactly 25 CPM delivers about 25 x 0.92 = 23 CPM in the building. It misses. Then ask the follow-up: what would you have to run at to guarantee 25 with that slippage? Size the no-slip theoretical rate up to about 25 / 0.92 = 27 CPM, and that headroom is the margin. Same calculator, same 25 CPM target, two very different designs. The one with no margin passes on paper and jams on the floor. Make them feel that in one calculation.
The failure mode this lesson is built to prevent is the student who treats a calculator output as a specification. It shows up first in the strong-math students, who take the clean number and move on without margin. Watch for it and drive them back to the solutioning-versus-final-engineering distinction every time. Signs:
Keep the class at Gap Produced, Theoretical Rate, Pitch, and the stress test. Those are the whole scope of this lesson. When a strong student pushes into CFPM, SGR, required sorter speed, the model-minimum or geometric gap check, or takeaway spur speed, that's the right instinct at the wrong time. Redirect: that's final engineering, Lesson 25 in Part VI, and it needs a confirmed rate in writing before it means anything.
The reason to hold the line isn't tidiness. A solutioning conversation that drags in final-engineering precision slows the whole design down and sets specs on inputs that aren't confirmed yet. At this stage you're confirming the flow can carry the rate. You're not sizing the sorter. Say that out loud when you redirect, so the deferral reads as discipline, not as content you're withholding.
Read Dana's throughput lines aloud: current peak 18 CPM, design target 20 CPM for three years of growth. Then make the room defend the call. Why design to 20 and not to today's 18? A student who can explain that the extra two CPM is deliberate headroom against a documented projection understands design rate. A student who just repeats the number Dana said hasn't made the decision, they've copied it.
Then push the harder half: full peak, or a percentage of peak the customer supplements with temporary labor? Both are valid engineering answers. Make them pick one and defend it out loud, and make them say where it gets written down. The point isn't which they choose. The point is that they chose on purpose and can defend it. Leaving it implicit is the one answer that fails.
The margin habit you're building here is the one that gets tested hardest later, in Part VI. Lesson 24 comes back to slippage and margin as a discipline, and Lesson 25 turns these same three outputs into locked specifications through the full Calc Logic Guide sequence. The students who internalize margin now walk into those lessons ready. The ones who treated the calculator as a black box get exposed there.
Don't tell them that's coming. Let the payoff land when it lands. Your job this session is to make margin feel like something a professional simply does, not a rule to memorize. The student who applies it without being reminded is the one you're growing.