Levers
A lever is a setting you expect to change often. Mark it once, give it a sensible range, and it's ready every time you build a what-if.
Why levers help
On any engagement, a few settings carry the whole conversation: nurses on shift, agents per hour, machines on the line. Those are your levers. Marking them does two things:
- It records which decisions are actually open, with the range the client will accept.
- It saves clicks. Each lever shows up as a one-click choice in New what-if.
You don't need a lever to test something. Any setting in the what-if builder can be changed without one. A lever is a shortcut and a record of intent.
Add a lever
- Select an element and open its Levers tab.
- Tick the setting. Quodsi fills in a label and a starting range.
- Edit the Label so it reads well, such as "Triage nurses".
- Choose how to Sweep it: for example, Set to or Multiply by.
- Set min, max and step to the range your client would really consider.
Untick a setting to stop using it as a lever. The levers are saved with the model.
Where levers are available
| Element | Levers tab appears in | Settings you can mark |
|---|---|---|
| Activity | Basic | Capacity, Inbound queue capacity, Outbound queue capacity, each step's Processing time. Priority needs Advanced. Breakdown and cost settings appear when those features are on. |
| Generator | Basic | Inter-arrival duration or Volume, depending on the generator type. Entities per creation, Periodic occurrences and Max entities are for Rate generators and need Intermediate. |
| Resource | Basic, though resources themselves appear from Intermediate | Capacity. Cost settings appear when financial tracking is on. |
| Connector | Basic | Weight |
| Model | Intermediate | Replications, Run length, Random seed, Warm-up length, and the starting value of each model or entity state of type number, true/false or category |
A lever needs a range or a list of values to try. Numbers and times sweep a range. A State's starting value can be a lever too, as described below. A setting that doesn't apply right now stays hidden. For example, Capacity is hidden when a work schedule sets it, and cost settings are hidden until financial tracking is on. If nothing applies, the tab says No levers apply to this element's current settings.
A hidden setting keeps any lever you already made. It stays listed, greyed, with the reason, so you can edit or untick it.
State starting values as levers
A state's starting value can be a lever. Use it when a value you set once drives the model, such as a mode that switches a route or a starting stock level. Only model and entity states of type number, true/false or category qualify. See Changing a starting value in a what-if for which states, and when a change has no effect.
- Two places, one lever. Tick Lever in the state's form, or tick the state's row in the model's Levers tab. Both edit the same lever, so you never get two. A state you create on the spot from a connector condition can be made a lever right away.
- Number levers sweep a range, with min, max and step, like any other lever.
- True/false and category levers sweep a list of values. A true/false lever tries both true and false. A category lever tries every category. Untick the values you don't want to try.
- A value that no longer exists. If you remove a category, or delete the state, the lever keeps the value. It's shown greyed with (missing), and the run skips that change. See Skipped changes.
- By goal. The suggestions under By goal don't offer State starting values.
Use levers in a what-if
In New what-if, your levers appear first in the choose a step menu. Picking one fills in the setting, how it's swept and its values.
If the model has levers and the what-if is empty, you'll also see Add all my levers. It adds a change for each lever at once. If that's more scenarios than a study can hold, Quodsi tries them one at a time instead.
Where else levers show up
- Studies from a bottleneck. When you press Study in Flow Analytics, Quodsi uses a Capacity lever's range if you've set one with Set to. Otherwise it starts one step above the current capacity and goes up to about double.
- Tradeoff View. Levers a study swept appear in the Levers group of the axis picker. You can plot Capacity against throughput directly. Only number levers can be an axis for now: a true/false or category state lever has no place on one, so pick another axis for those studies. See Tradeoff View.
Example
In a clinic model, the client will only consider two to five triage nurses. On the Nurse resource, tick Capacity, label it "Triage nurses", and set min 2, max 5, step 1. Now every what-if starts from a range the client has already agreed to. A study run on that lever shows where one more nurse stops helping.
Common mistakes
- Marking everything. Levers are for decisions that are really open. Twenty levers tell you nothing about what matters.
- Setting a range the client can't act on. Stay inside the budget and floor space they really have.
- Forgetting the switch. A cost lever does nothing until financial tracking is on. See Costing.