A fulfillment center at the morning peak. Pickers walk the aisles, totes queue on the conveyors, packers race the trucks. The same nine people can be arranged several ways, and one arrangement clearly beats the rest.
Where should the labor go? The results cover 07:00 to 09:00. The building opens at 06:30 with 50 orders left from overnight, so by 07:00 the racks are stocked, pickers are out on trips and totes are riding the conveyors; then a morning wave of new orders arrives. Trucks leave every 30 minutes, and an order has to make the first truck that leaves at least 30 minutes after it comes in.
As set, six people pick and three pack. Picking keeps up; packing doesn’t. Totes back up on the conveyors, and late orders ride the next truck. Adding a person is the obvious answer. The model lets you test the less obvious ones first.
Same orders, same aisles, same trucks. Only the labor changes. Moving one picker to packing doesn’t help by itself, because picking becomes the constraint. Moving one picker to packing and picking two orders per trip makes every truck with the same nine people, ships the most orders of any plan here and has the lowest labor cost per order. Adding a tenth person also makes every truck, but ships fewer orders at a higher cost per order.
| Labor plan | Made its truck | Shipped 07:00–09:00 | Order cycle | Labor per order | Most totes on the conveyors |
|---|---|---|---|---|---|
| As set: 6 pickers, 3 pack stations | 95.1% ± 2.7 | 228 | 25.8 min | $1.90 ± 0.02 | 34 |
| Open a fourth pack station (10 people) | 100.0% ± 0.0 | 256 | 15.7 min | $1.87 ± 0.03 | 6 |
| Same 9 people: 5 pickers, 4 pack stations | 93.8% ± 3.5 | 225 | 26.6 min | $1.92 ± 0.03 | 5 |
| Same 9 people: 5 pickers, 4 pack stations, 2 orders a trip | 100.0% ± 0.0 | 262 | 15.2 min | $1.65 ± 0.03 | 8 |
| Batch picking with 3 pack stations | 94.1% ± 3.1 | 227 | 27.0 min | $1.90 ± 0.01 | 37 |
Each row is the mean of 20 runs from seed 1 (± = 95% confidence interval), run 2026-11-09 in the same sandbox as the workspace. Each run starts at 06:30 so the building is already busy at 07:00; the results count 07:00 to 09:00. Labor is $24 an hour for pickers and packers alike.
Open the model and the decisions sit at the top as plain numbers: pickers, pack_stations, batch_size, the overnight backlog, the truck schedule and the wage. Change one, press Run, and watch the animation and the results panel. Set Runs to 5 or more before you decide anything: one run is one morning, and mornings vary. Your edited copy is saved privately in your account, with its history.
The model is written in chiaha-SLX, a simulation language for models written as code. The animation isn’t a separate tool: the model writes it, line by line, as it runs. More about the language on the chiaha-SLX page.