---
title: "Expression controls"
description: "Lesson 7.7 of Creator Terminal's lesson films (Going deeper): Give a circle a named slider, link its scale, and see why exports keep the motion as keys."
canonical: "https://terminal.lottiefiles.com/expression-controls/"
last_updated: 2026-10-27
---

# Expression controls

> Lesson 7.7 of Creator Terminal's lesson films (Going deeper): Give a circle a named slider, link its scale, and see why exports keep the motion as keys.

- The film (1:43): https://terminal.lottiefiles.com/media/7.7-expression-controls/609fa3097582/7.7-expression-controls.mp4
- Vertical cut: https://terminal.lottiefiles.com/media/7.7-expression-controls/90feea45c146/7.7-expression-controls-vertical.mp4
- Captions: https://terminal.lottiefiles.com/media/7.7-expression-controls/4c3568cac609/7.7-expression-controls.vtt
- The page: https://terminal.lottiefiles.com/expression-controls/

## In this lesson

### A controller layer (0:10)

Our slider needs a home. Press colon, type add controller, then press return. In the rail, this empty layer holds controls; it draws nothing.

### Store a value (0:22)

Now let's store our starting size. Click slider. Click its name, type Size, and press return. Click its value, type fifty, and press return. The circle stays unchanged for now.

### Key the slider (0:35)

We'll animate that from fifty to a hundred. Click the key marker. On the ruler, click one point five seconds. In the rail, click the value, type one hundred, and press return. On the score, look at Size. It has two keys.

### Choose the target (0:51)

Now we'll make Scale follow Size. Click the circle. In the rail, click a Scale number, then press escape to choose that property. In the palette, press colon, type follow, and press return.

### Pick the source (1:04)

Then choose our slider as the source. Click the Controls Size row. A driven Scale row appears. The slider now drives the circle.

### Play the result (1:14)

Now that it's linked, let's try it. Press zero, then space. There it is. The circle grows from half to full size. Press space to pause. The slider supplies both scale dimensions.

### Deliver the motion (1:27)

We'll deliver that motion as keys. Let's check the limit. Click more, then live in dotLottie. Below, the message explains why.