# Understand a PLC project you inherited

> How to get oriented in a large Studio 5000 project you did not write, using a project tree, graphical ladder and an AI agent that cites the rungs behind each answer.

Source: https://orbiscontrols.com/guides/understand-an-inherited-plc-project

You open a project with thousands of tags and dozens of programs, written by someone else, and someone asks why a pump stopped. This is the situation Orbis is built for.

## 1. Get the shape of the project

Open the `.L5X` or `.ACD` file. The project tree lists the controller, programs, routines, Add-On Instructions, data types and I/O configuration. Tag tables show controller and program tags. See [Open a project](https://orbiscontrols.com/docs/open-a-project).

## 2. Read logic as ladder

Routines open as graphical ladder with the glyphs you know from Studio 5000: contacts, coils, instruction boxes and branches. Structured text, function block and sequential function chart routines open too.

## 3. Ask instead of searching

Ask the agent in plain words why a rung trips, where a tag is written, or what happens when a level goes high. Each answer cites the rungs and tags it used. See [Ask the agent](https://orbiscontrols.com/docs/ask-the-agent) and [Find where a tag is written](https://orbiscontrols.com/guides/find-where-a-tag-is-written).

## 4. Change it with a review

When you know what to change, edit a working copy by hand or ask the agent, then review the change as ladder before it goes back to Studio 5000. See [Review changes](https://orbiscontrols.com/docs/review-changes).

Orbis is free during the beta. Start with [Install Orbis](https://orbiscontrols.com/docs/install).