If you want to get a closer (or wider) look at your diagram, you can use the Zoom dropdown in the toolbar to set the zoom.

The + Zoom and – Zoom buttons give you a tool that allows you to zoom in (or out) on a specific area of the diagram by clicking the Drawing Canvas.

You can also zoom in a very specific are by selecting the + Zoom tool and drawing a rectangle around that area with a click-drag-release.