To find out how long a chord is by looking at its arc, you can use some basic facts about circles. Here’s a simple guide to help you:

1. Know the Basics: The length of a chord depends on the radius of the circle and the angle at the center of the circle that connects to the arc.

2. The Formula: If you have the radius (that's the distance from the center to the edge) and the central angle in degrees, you can find the chord length with this formula:
   $C = 2r \sin\left(\frac{\theta}{2}\right)$
   Here, $C$ is the chord length, $r$ is the radius, and $\theta$ is the central angle.

3. An Example: Let's say the radius of your circle is 10 cm and the angle is 60 degrees. Here’s how you calculate the chord length:
   $C = 2 \times 10 \sin\left(\frac{60}{2}\right) = 20 \sin(30) = 20 \times \frac{1}{2} = 10 \text{ cm}$

By following these steps, you can find the length of any chord as long as you know the radius and the central angle! It's really that easy!