# Overview

Learn how stock moves, warehouse levels, serialized items, replenishment, and cost allocation work.

Source: https://support.toolingmetrics.com/en/inventory/overview/

- [How the inventory model works](https://support.toolingmetrics.com/en/inventory/overview/inventory-model.md): What move lines are, how quantity types are calculated, and why the numbers you see are always current.
- [Why the warehouse has five levels](https://support.toolingmetrics.com/en/inventory/overview/warehouse-hierarchy.md): Why the five-level structure exists and how it enables automatic purchasing and precise restocking across multiple sites.
- [Serialized vs. non-serialized items](https://support.toolingmetrics.com/en/inventory/overview/serialized-vs-non-serialized.md): When to track individual pieces and when bulk quantity tracking is sufficient.
- [How automatic replenishment works](https://support.toolingmetrics.com/en/inventory/overview/automatic-replenishment.md): How stock rules, the inventory scheduler, and PO confirmation work together to keep warehouses stocked automatically.
- [How tool cost allocation works](https://support.toolingmetrics.com/en/inventory/overview/cost-allocation.md): Why different cost methods exist and how categories let you configure them once for many items.
- [How automatic service pick works](https://support.toolingmetrics.com/en/inventory/overview/automatic-service-pick.md): How confirming a Service Order can automatically assemble the Service Picks and Return Lists for exactly the items that need vendor service — no manual hunting required.

How Tooling Metrics mirrors each physical tool is in [The tool digital twin](https://support.toolingmetrics.com/en/start-here/digital-twin/), in Start here.