PIMSLS has a viewport to view the slides. The viewport is set to display a single image by default, but can be split into a grid.
The video below will take you through the basics of working with the grid system.

Note that as an alternative, you can also have different viewports open in separate panels. If you work with panels, you can still reorganize them, and each panel can have its own custom size too.

The “GRID” tab consists of 6 sections:

1. Size
2. Synchronize
3. R/C (rows and columns)
4. Slide viewing properties
5. Snapshot
6. Share