Division Selector

Controls the grid size and the visible time range of the waveform. In Sync mode the grid aligns to bars, in Free mode it determines how much audio fits on screen. Available divisions: 1/4, 1/2, 1, 2, 4, and 8 bars.

The T button on the right switches the grid to triplet subdivisions.

Shortcut

You can quickly change the division with Alt + Mouse Wheel (on macOS: ⌥ Option + Mouse Wheel).