The Magnifier tool

The magnifier tool is a kind of floating window which you can drag around. It allows to into parts of the layout.

Invoke the magnifier from the grid's or select 'Grid | Magnifier'. It will open with a default size of 240x240 pixels and a scale factor of 2:1.

You can:
Increase the scale factor by clicking inside the magnifier.
Decrease the scale factor by Alt-clicking inside the magnifier.
Drag the magnifier window around. The magnified area starts at the window's top/left position.
Resize it by dragging the triangle in the bottom/right corner.
Close it by clicking inside the grid but outside the magnifier window.