# Define Expression Fields in Printing?
**YouTube:** [How to Define Expression Fields in Document Printing?](https://www.youtube.com/watch?v=3V3yjx4_fVU)
## How to Define Expression Fields in Document Printing?
In this tutorial, we’ll learn how to **design and use expressions** in the Designer Printing Format of Logic ERP.
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### Steps to Create Expressions
* From the **Menu Bar**, go to **Continuous Printing → Sales Bill Print Designer and Printing**.
* Select the **required configuration** and sales bill, then click **Refresh**.
* Open the **Design Window**.
* Go to the **Properties Menu** (bottom left) and open the **Expression Designer**.
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### Building Custom Expressions
#### Example 1: Sum Function
* Click on the **SUM function**.
* Browse and select the required fields.
* The system will calculate their total automatically.
* Use the **equals (=) symbol** to check the result instantly.
#### Example 2: Convert Number to Words
* Select **Footer Details → Total Net Amount**.
* Insert this field into the designer.
* Apply the conversion function.
* Using the equals (=) symbol, you’ll see the amount displayed in words.
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### Saving and Using the Expression
* Once your expression is complete, click **OK** to exit the Expression Designer.
* Click on the **Save Expression** button.
* Give your expression a **suitable name** (e.g., *Amount in Words*).
* The new expression will now appear under the **Expression Table** in the Properties menu.
* Right-click on it → **Insert** into the printing layout.
* Save the changes.
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### Preview
* Go to **Print Preview**.
* You’ll see the new expression (e.g., Amount in Words) correctly displayed in the bill format.
