You can make the notation bigger or smaller by clicking and dragging the “Zoom level” slider in the player’s settings. You’ll find the settings menu by clicking the gear icon in the lower right.
If “Respect author’s stave breaks” is unchecked (see here), Soundslice actually re-engraves the music. At one zoom level, you might have two bars per system; at another, that might get increased to three or four. Everything is repositioned for you on the fly.
If “Respect author’s stave breaks” is is checked, Soundslice will not re-engrave the music. Zooming in Paged layout simply zooms the entire page in/out:
Zooming on mobile
On mobile or tablet, you can zoom by pinching your fingers on the notation.
Careful, this can be addictive.