Zoom 

The Zoom Tool is used to show a close-up view of a section of the current video image. This tool behaves like one of the digital illustration tools. When you click the Zoom button, the cursor becomes a magnifying glass. Move the cursor over the video, then click and hold the mouse button to display a “window within a window” magnified view. While holding the button down, you may move the mouse and the magnification window will follow. 

The magnification window is intentionally “offset” slightly up and to the left to prevent the cursor from obscuring the intended center point of interest. Here’s an example: