PIMS LS 3.0.1

The Size toolgroup contains icons for changing how many cells are visible in your viewport

In the top row you can see icons for making a 1×1, 2×2, and 3×3 viewport grid, with 1, 4 and 9 images - respectively.
When you click one of the options, the software will ask if you want to keep the current images or replace them.

The custom size button allows you select how many cells tall and wide you want your viewport to be.