For bar charts, line charts, and pivot tables, the content of the visual can be larger than the size that you want the visual to be.
In these cases, scrub bars appear so you can either reduce the data that is displayed or scrub through it. This process is similar to the way that you can scrub through a video.
To reduce the length of the scrub bar, hover over one end of it until the cursor changes shape. Then drag the widget to make the scrub bar larger or smaller. To scroll through the data, click and hold the scrub bar and slide it toward the end that you want to see.