> ## Documentation Index
> Fetch the complete documentation index at: https://docs.simcel.io/llms.txt
> Use this file to discover all available pages before exploring further.
# Running Simulation
> Launch and monitor supply simulations to validate plan feasibility and compute constrained KPIs.
## Purpose
Running a supply simulation in SIMCEL is a critical step to evaluate the alignment between your supply plans and demand forecasts. This guideline helps you navigate the process effectively, so you achieve accurate and meaningful results.
## Prerequisites
Before running a supply simulation, make sure the following prerequisite is met:
* **SIT levels** - You have finished setting the SIT (Sales In Target) levels per distributor and product. This defines the expected Sales In levels for each scenario.
### Preparation
Create or edit the scenario you want to run the simulation for.
Ensure that the scenario is associated with the appropriate supply plan. If it is not already imported, upload the supply plan scenario in the ETL screen.
## Running the simulation
Click **Run Simulation** in the scenario dropdown menu.
This action triggers the simulation process with the following steps.
### 1. Validate Sales In
* SIMCEL performs a sanity check on Primary Sales by checking whether any negative value exists.
* A popup warning may appear to inform you about the exclusion of negative values. If this happens, click **Confirm** to continue, or **Cancel** if you would prefer to adjust your SIT parameters.
### 2. Run simulation
* **Initial stock determination** - The simulation begins by determining the initial stock level, using the closing stock of the period before the simulation start date.
* **Sales and inventory simulation**:
* For each month, the tool adds the supply quantity to the beginning inventory.
* The resulting inventory level is compared with the Unconstrained Sales In to determine demand fulfillment.
* If the inventory level meets or exceeds the unconstrained demand, the Constrained Sales In equals the Unconstrained Sales In. If not, it is limited to the available stock.
* The closing stock for the month is calculated as:
```text theme={null}
Closing stock = Opening stock + Supply quantity - Constrained Sales In
```
### 3. Metrics calculation
* SIMCEL calculates all the metrics used to generate the simulation output and atomic KPIs.
* This ensures that all metrics accurately reflect the impact of supply constraints on distributor demand fulfillment.
### 4. Simulation output
Once the simulation is complete, you can access the output files of each scenario. These include:
* **Simulation Sales In** - Contains Constrained Sales In data for each distributor.
* **Demand Fulfillment Metric** - Breaks down distributor demand into individual orders, showing fulfillment status.
* **Detailed Inventory Metrics** - Provides a comprehensive record of inventory levels, including opening and closing stocks, quantities received, quantities shipped, and any adjustments.
* **Atomic KPIs** - Offers granular data, including product details, distributor information, and location data, for in-depth analysis.
### 5. Interpreting KPIs
Navigate to the **Business Explorer** page to review the performance KPIs generated by SIMCEL.
### 6. Adjusting plans based on insights
Use the insights gained from the simulation to make necessary adjustments to your supply and demand plans.
* After you validate the Primary Sales In, the simulation starts running. A dialogue indicates the steps and the current simulation progress.
* You can temporarily hide this dialogue by clicking **Keep working**.
* After hiding the dialogue, you can still monitor the simulation's progress by checking the scenario tab. A loading indicator appears right next to the scenario being triggered.
## Constrained SIT
Once a supply simulation is complete, you can access detailed metrics to analyze the outcomes and make informed decisions. The SIT table lets you toggle between unconstrained and constrained metrics, giving a comprehensive view of supply chain performance.
The primary outcome of the simulation is the **Constrained Primary Sales**, which is the volume of products the company can supply to its distributors. Based on this revised sales input, the tool recalculates the following metrics.
### 1. Constrained Secondary Sales
* Represents the sales to end customers, considering the available supply from distributors after accounting for constraints.
* Indicates how much of the distributor's demand can be fulfilled based on the available inventory.
### 2. Constrained Stock Value
* Shows the inventory levels at the end of each period after meeting the Constrained Sales In.
* Helps you understand the remaining stock and plan for future supply needs.
### 3. Constrained Stock Days (SIT)
* Reflects the quantity of stock currently at the distributors, expressed in days of sales.
* Provides insight into inventory levels in a normalized way.
- If any of the selected scenarios have not been simulated, switching to Constrained mode shows no data for that scenario.
- If you modify the input - for example by choosing a new supply plan or setting new unconstrained metrics - you can re-run the simulation with the updated inputs.
